BT Cellnet, the second largest mobile phone operator in the UK, claimed leadership of the Wap sector with 420,000 subscribers by the end of September.
Mobile phones using the Wireless Application Protocol (Wap) allow users to browse a cut-down version of the internet.
But the company again lost ground in the overall mobile phone market to third place Orange, which on Monday claimed growth of 1.1 million in subscriber numbers between June and September.
One2One proved the fastest growing operator, with 1.12 million new subscribers over the quarter.
While more than 3.5 million Britons overall signed up to mobile phones over the summer, BT Cellnet's declining share of new trade threatens the firm's place in the operators' table, analysts said.
Cellnet 'demoted'
"The danger is that Cellnet is going to fall into third place," said Luke Norbury of UBS Warburg. "That could happen in the next quarter."
*At 30 September 2000
But David McGlade, BT Cellnet's managing director since Sunday, said BT Cellnet would benefit from its prominence in Wap.
"Wap is proving popular with customers and already providing additional revenues to BT Cellnet," he said.
"We're going to see a lot of action in this area as we continue to drive the development of the mobile internet experience."
Vodafone confident
Vodafone, the world's largest mobile phone company, is reported to have less than 100,000 Wap users.
*June-September, over quarter before
But company spokesman Mike Caldwell, who declined to confirm the figure, said many phone firms had held back Wap promotion efforts while monitoring the development of the sector.
"Cellnet marketed their phones a lot earlier than other companies," he told BBC News Online.
"The other companies are expected to have major marketing drives on the run up to Christmas."
It was "early days" to suggest that BT Cellnet had stolen a march on Vodafone in the Wap market.
"We have led them in the mobile phone market since 1986," Mr Caldwell said.
Barrier broken
Vodafone has become the first operator to exceed 10 million mobile phone subscribers in the UK, the company's figures for June to September showed on Wednesday.
Vodafone, which added 877,000 to its UK subscriber total over the quarter, claimed 65.75 million customers worldwide, and is on target to achieve 50% customer growth for the fourth year running, chief executive Chris Gent said on Wednesday.
"The past year shows yet further excellent growth in our customer bases around the world," he said.
German operations, boosted by the purchase of Mannesman for £112bn earlier this year, achieved particular growth, adding 2.73 million subscribers.
Subscriber figures for joint operations, eg with Alcatel in Spain or Omnitel in Italy, are adjusted according the level of Vodafone's investment.
Orange booms
Orange, which France Telecom is to float later this year, on Monday claimed 1.1 million growth in subscribers between June and September.
"These results complete four consecutive quarters of record growth for Orange, during which the customer base has more than doubled," deputy chief executive Graham Howe said.
One2One, bought by Deutsche Telekom last year, now claims more than 7 million UK subscribers.
Shares in Vodafone closed at 249.75p, down 2.00p, in London on Wednesday.