Viewers should notice improvements in picture and sound quality, particularly in the case of high-definition (HDTV) broadcasts. (To get the full effect, you’ll need a high-definition set, and the broadcaster and, if applicable, cable or satellite provider must provide a high-definition signal.)

Digital transmissions make more efficient use of the broadcast spectrum, leaving more of the airwaves available for additional channels or interactive data services.

When analog TV broadcasts end, broadcasters will return those frequencies to the federal government. Some have been pre-allocated to public-safety uses, including communications systems for police and fire departments. The government is likely to auction off much of the rest to wireless companies and others for commercial uses.

Source: www.dtvfacts.com

In comparison, analog television produces a total of about 210,000 pixels. Broadcasters and cable providers can choose which format of DTV they transmit, and most DTV's and new HDTV set-top boxes will be able to receive the signal regardless of which format is transmitted. Note, however, that your standard analog TV set will not be able to receive DTV signals (neither HDTVnor SDTV).

The only televisions that have DTV turners are those that since about 1998, have been sold as having an integrated or “built-in” DTV or HDTV broadcast turner. (An HD set sold as a “monitor” or “HD-ready” is capable of displaying HDTV but does not have a built-in HDTV turner) Most TVs with analog turners are now required by the FCC to also be marketed with built-in or separate DTV or HDTV turners – this will soon be a requirement for all TVs.

If your television set is labeled as a “Digital Monitor” or “HDTV Monitor,” or as “Digital Ready” or “HDTV Ready,” this does not mean it actually contains a digital tuner.

If your television set is labeled as “analog” or “NTSC,” and is NOT labeled as containing a digital tuner, it contains an analog tuner only.

If you cannot determine whether your television set or other television equipment contains a digital tuner, you are advised to check your equipment for the manufacturer name and model number, and then contact your consumer electronics retailer, or the manufacturer, to determine whether it contains a digital tuner. This information also may be available online through the manufacturer's website.

Some of the TV's manufactured from 2004 to 2006 were advertised as “HD-ready” or “HDTV monitor” sets. That means they can display digital and high-definition signals, but they need help getting those signals in the first place. You’ll still need a special converter or a cable TV connection.

Countries that are already switched-off to digital television are:

Luxembourg was the first country to complete the move to digital broadcasting on September 1, 2006.
Netherlands moved to digital broadcasting on December 11, 2006. The switch-off was helped greatly by the fact that about 90% of the households have cable that continues to use analog distribution.
Finland ceased analogue terrestrial transmissions nationwide at 4am, September 1, 2007 (switch-off was previously planned for the midnight after August 31 but a few extra hours were added for technical reasons). Cable TV viewers continued to receive analogue broadcasts until the end of February 2008.
Andorra completed its switch-off on September 25, 2007
Sweden The switch-off of the analogue terrestrial network progressed region–by–region. It started on the island of Gotland on September 15, 2005, and was completed on October 15, 2007, when the last analogue SVT1 transmitters in Scania and Blekinge were shut down. Cable distributors are allowed to continue broadcasting analogue television.
Switzerland began with the switch-off on July 24, 2006 in Ticino and continued with Engadin on November 13, 2006. The switch-off was completed on 26 November, 2007.
Austria began analogue switch-off on March 5, 2007, progressing from the west to the east and finishing the switchover on May 5, 2008.

Countries that are currently in process to switch-off to digital television are:

Australia: The Australian government originally planned a switch-off in 2008. This has now been delayed to 2009 for metro areas and to 2013 for the regions. Until that time, free-to-air stations will be simulcast, along with digital only channels like ABC2. Since 1999, legislation has required all locally made free-to-air television transmissions to be in 16:9 widescreen format. Cable television networks began simulcasting in 2004 and analog cable services were switched off in April 2007.
Bulgaria will complete its analog switch-off in December 2012.
Brazil began free-to-air HD digital transmissions on, after a period of test broadcasts, on December 2, 2007 in São Paulo, expanding in January 2008 to Brasília, Rio de Janeiro, and Belo Horizonte. Digital broadcasts will be phased into the other 23 state capitals by the end of 2009, and to the remaining cities by December 31, 2013. Analogue and digital simulcasts will continue until June 29, 2016, when analogue will be discontinued. The main broadcasters (Globo, Record, Band, SBT and RedeTV!) are simulcasting in analogue and digital broadcast, in standard definition and 1080i high definition.
Belgium: the situation is rather complex, as media regulations are under regional legislation. The Flemish region has announced that it will switch off analogue television on December 31, 2008, because coverage is already at 99 percent. The Wallonian Region has not yet announced a date and is expected to follow the European dates because the geographic difficulties to cover the whole region. In Wallonia there is already an 80 percent DTT coverage.
Canada: The main FTA broadcasters (CBC, CTV, and Global) have launched HD streams of their programming in limited markets such as Toronto and Vancouver. Originally, unlike in the other countries, Canada was allowing the market to determine when the analogue switch-off begins. As a result, currently analogue and digital broadcasts co-exist, with virtually the only way to receive Canadian digital TV in most areas being via cable or satellite TV. In Toronto it is possible to pick up DTV over the air; in Montr̩al, Ottawa and Quebec City a partial set of channels (most often CBC only) are offered Рprimarily as a vehicle for limited HDTV deployments. Much of Canada has some over-the-air access to US border stations, most of which offer ATSC DTV. Signal strength and quality varies widely. New TV's and DVD recorders often include ATSC tuners but basic converters for existing NTSC TV's typically are not readily available locally. As of May 2007 there are fewer than 20 digital television stations in Canada. On May 17, 2007, the Canadian Radio-television and Telecommunications Commission (CRTC, Canada's broadcasting authority) ruled that television stations would be forced to switch to ATSC digital broadcasting by 31 August 2011, with minor exceptions in remote areas where analogue transmissions will not cause interference.
China: The switch-off is scheduled to be in 2015.
Czech Republic started the switch-off in September 2007 and should finish by September 2010. A broadcast law amendment which would change this is awaiting approval. The areas of Brno, Domažlice and Ústí nad Labem have already switched off.
Denmark began digital transmission in March 2006 and the analogue network will be closed at the end of October 2009.
Estonia has full digital signal by the 1st of August 2008, but analogue broadcasting still continues for the first of two public TV channels (ETV) while the second is available digitally.
France will have completed the switch-off in 2011. 80% of the population will be able to see TNT in 2008.
Germany started the switch-off in the Berlin area, beginning on 1 November 2002 and completing on 4 August 2003. It has also been completed in Bremen and Hamburg. “Simulcast” digital transmissions have started in other parts of the country, in an effort to prepare for a full switchover. The switch-off is planned to be completed by the end of 2008.
Greece: the switch-off will complete after the end of 2011.
Hong Kong's analogue broadcasting is planned to be switched off by 2012.
Hungary is scheduled to switch off analogue broadcasting between 2010 and 2013.
Ireland's broadcaster RTE plans to make digital television available to most of the population by 2010, and the switchoff is planned to be complete by 2012.
Italy's government aims to complete the digital switchover by 2012.
Japan is also running an intense nationwide campaign announcing the planned switchover to digital on July 24, 2011. Many television stations around the country are already broadcasting simultaneously in digital, or are planning to start digital broadcasts by 2007.
Kenya's Communications Commission of Kenya (CCK) announced that the country will start digital broadcasting in 2008 following preliminary work by the government. Kenya will be among the first countries in Africa to implement digital broadcasting.
Mexico has a 20-year plan to switch, with the target year of 2022 for the analogue shut-off. Some digital signals are already on-air, the first being Tijuana's XETV – an English-language affiliate of The CW serving primarily San Diego, California. Groups of cities which are required to simulcast digitally are added in descending order of size, with full coverage of the smallest centers required for 2021.
Malaysia: Information Ministry was planning to shut down the country's analogue television system in phases beginning from 2009 and set to convert to full digital TV in 2015.
New Zealand: It was announced on the 29 November 2007 that the analogue TV broadcasts will end within the next 6 to 10 years and expect a switch off date to be announced by 2012. Digital broadcast via Freeview become available late 2007.
Norway: The switch-off of the analog transmissions started in March 2008 and will the progress region-by-region. The last analogue transmitters are scheduled to close down by the end of 2009.
Portugal's government aims to complete the digital switchover by 2012; digital broadcasts will start in 2008.
Philippines: the National Telecommunications Commission will terminate all analogue television transmission on December 31, 2015. ABS-CBN, the country's largest TV network is planning to supply set-top boxes to areas in the Metro Manila market where the current signal of the network is weak where it will give its stations in the digital platform.
Russia has announced that the switch-off is to be completed in 2015.
Slovakia: the government aims to complete the digital switchover by 2012.
Slovenia: the switch-off will be completed in 2010.
South Africa will start switch-off in November 2008 in preparation for the 2010 FIFA World Cup and should be completed by mid 2011.
South Korea's analogue transmissions will be terminated nationwide on December 31, 2012.
Spain: the switch-off will be completed on or before April 3, 2010.
Ukraine: analogue transmissions will be terminated on 17 July 2015.
United Kingdom: The first switchoff of analogue television was on 30 March 2005, in the villages of Llansteffan and Ferryside in Wales. However, it was partially unsuccessful as residents insisted that BBC Two Wales be left broadcasting in analogue as they felt that the digital replacement, BBC 2W, which opts out from BBC Two from 20:30 to 22:00 on weekdays, shows too much Welsh programming The switch-off of all analogue terrestrial TV broadcasts resumed again on October 17, 2007 with Whitehaven in Cumbria and will now proceed region by region. The last regions will be switched off in 2012. In the UK, the free-to-air digital broadcasts are branded as Freeview.
United States: By no later than February 17, 2009, all full-power U.S. power television will be digital, and analogue transmissions terminated, according to legislation setting this deadline signed into law in early 2006.

Source: wikipedia.org