AT&T, the No. 2 U.S. mobile service provider, said the price cut took effect on Wednesday. The company is the exclusive U.S. wireless carrier for the phone, made by Taiwan's HTC Corp and launched on April 12.
An AT&T spokeswoman said price-cutting promotions are not unusual. But operators typically wait longer than a few weeks after a launch before discounting phones.
Richard Windsor, an independent analyst, said in his Radio Free Mobile blog that the price cut was a worrying sign for social network Facebook and its future in mobile.
"The final verdict on Facebook Home was brutally handed down yesterday with AT&T slashing the price of the HTC First from $99 to $0.99," Windsor said.
(Reporting By Sinead Carew; editing by John Wallace)