NEW YORK (Reuters) - T-Mobile USA, the fourth biggest U.S. mobile service provider, said on Friday that it would start selling the highly anticipated and much delayed BlackBerry Z10 touchscreen smartphone to its business customers on March 11.

The U.S. unit of Deutsche Telekom said business customers could get delivery of the device by the end of next week. It declined to give a date for the consumer launch except to say that it would be before the end of March.

BlackBerry, formerly known as Research In Motion, already sells the device in more than 20 countries but its reception in the United States, its former stronghold market, is seen as a key step. However, U.S. consumers have had to wait much longer for the device than other countries like Britain.

Bigger rivals Verizon Wireless and AT&T Inc declined to reveal their Z10 launch dates on Friday and Canada's BlackBerry declined comment.

BlackBerry, a one-time smartphone pioneer, has bled market share to the likes of Apple's iPhone, as well as Samsung's Galaxy product line and other devices powered by Google Inc's market-leading Android operating system.

In a make-or-break move to regain market share and return to profit, BlackBerry introduced the new smartphone to much fanfare in January. A more traditional BlackBerry with a physical keyboard will go on sale next month.

(Reporting By Sinead Carew; Editing by Nick Zieminski)