Fans of the T-Mobile G1 are in luck, as an executive has confirmed that the fourth-largest U.S. wireless carrier will launch successors later this year.

The G1 was highly anticipated at its launch last November because it was the first commercially available handset that used Google's open source Android operating system. The handset was met with mostly positive reviews, and it sold 1 million units in 61 days.

"As the year progresses there will be a significant number of HSPA-capable smart phones. We will be launching more G series phones and other products," said Neville Ray, T-Mobile's senior VP of engineering, in an interview with Fierce Wireless. "You will see us launch a data card product. This will be happening in the coming weeks and months."

The G1 features a large touch screen that slides out to reveal a full QWERTY keyboard. While this gives users multiple input options, some said the added bulk makes for an unpleasant design. Gadget blog Gizmodo has posted shots of a device that's reportedly the G2, and it ditches the keyboard for a slimmer, touch-only design.

If more G series smartphones come out in 2009, they will face a crowded field as multiple vendors are expected to release Android-powered handsets for various carriers. Samsung is reportedly readying an Android phone that will have a similar form factor to the Instinct, and it will be available for T-Mobile and Sprint in the first half of the year. Sony Ericsson, Motorola, and even navigation-device maker Garmin are also expected to have Android smartphones this year.

Many of these new devices will take advantage of T-Mobile's expanding 3G network. The carrier has already deployed its UMTS/HSPA network in more than 25 markets, and Ray said it's expected to be in more than 300 cities by the end of the year.