Sprint Nextel Corp. (S) will offer Google Inc.'s (GOOG) Google Voice on all Sprint phones, and it will allow customers to use their existing Sprint wireless phone number.

Google Voice, a phone forwarding and voicemail service, allows users to make and receive calls between their computers and phones after they install a voice and video software plug-in.

Sprint said it is the only carrier to allow the use of their existing mobile phone number without paying porting fees.

This spring, Sprint will begin selling the Nexus S 4G phone from Samsung Electronics Co. Ltd. (SSNHY, 005930.SE), and it will come preloaded with the Google Voice Android appplication.

Sprint has managed to stabilize declines in customers and revenue, but still doesn't carry Apple Inc.'s (AAPL) iPhone and has much weaker profit margins than AT&T or Verizon. A person familiar with the company's thinking told The Wall Street Journal on Sunday that Sprint is concerned that AT&T's acquisition of T-Mobile USA would leave the U.S. telecommunications market dominated by two companies and hurt Sprint's ability to compete.

Shares of Sprint were down 13% at $4.38 premarket. As of Friday's $5.05 close, the stock had risen 34% the past year.

-By Melodie Warner, Dow Jones Newswires; 212-416-2283; melodie.warner@dowjones.com