TerreStar Corp's majority-owned unit signed a deal with AT&T to launch the first fully integrated satellite smartphone, sending its shares up 39 percent to a 52-week high.

Users will be able to access voice and data services in the United States, Puerto Rico, the U.S. Virgin Islands and offshore coastal waters over either the AT&T cellular network or the TerreStar satellite network, said the unit, mobile communications provider TerreStar Networks Inc.

The service is intended to work as a user's everyday cellular smartphone device, with satellite access capability as a secondary option when needed.

TerreStar shares rose to a high of $2.95 before paring some gains to trade up 20 percent at $2.56 Wednesday morning on Nasdaq.

(Reporting by S. John Tilak in Bangalore; Editing by Anne Pallivathuckal)