Three wireless operators have emerged as the leading providers of advanced cellular data services in the U.S. and the eventual winner is still up for grabs, according to a study released Tuesday by market research firm Forrester.

The study found that AT&T Wireless, now a part of Cingular Wireless, jumped to an early lead with its nationwide EDGE network, with Verizon Wireless in second place and Sprint PCS in third place. However, those results are far from definitive in the long-term, Lisa Pierce, a Forrester vice president, said in a statement.

"Since the 2.5 and 3G market is relatively new in the US, we were not surprised that none of the providers were successful across all of the categories we evaluated," Pierce said. "As the market continues to evolve, there is significant opportunity for current leaders to stumble and challengers to move up.

For instance, while AT&T Wireless was first to market with its 2.5G EDGE network, it stumbled badly in terms of customer confidence in the last two years before its acquisition by Cingular closed last fall. Verizon Wireless, on the other hand, has been rapidly deploying its 3G 1xEV-DO network and has the best chance to become a market leader, the study concluded.

Cingular''s recent acquisition of AT&T Wireless and the announced merger of Nextel and Sprint offer the providers a new set of opportunities, according to Pierce.

"These mergers create additional opportunities for relative leadership positions to change over the next 12 to 24 months," she said.