Thousands of UK households using the Ionica telephone service have been urged to find another supplier or face having their phones cut off at the end of the month.
Telecoms watchdog Oftel said this week about 12,000 Ionica customers have not yet found a new operator and face losing access to emergency services and other vital telephone services.
Ionica, which operates in East Anglia, the Midlands and Yorkshire, went into administration last October after struggling to make money from its innovative radio wave telephony service.
The technology, developed by Nortel Networks, has been touted as a cheap way for operators to establish local networks without having to lay copper.
But problems have tainted the technology's reputation.
BT stepped in with #3 million in December to keep Ionica afloat while its customers arranged new suppliers. BT and other telephone companies offered special incentives in a bid to poach ex-Ionica customers.
But BT's charity ends on 28 February when Ionica will be shut down completely.
Oftel says time is running out for Ionica customers.
"I am concerned that a small number have not made firm arrangements with another operator. People should not wait until the last minute," said Oftel's director general David Edmonds.
BT claims to have poached 45,000 Ionica customers since October and its engineers have already plugged in more than half of them. BT is competing against cable companies including Cambridge Cable and NTL for the windfall business.
However, time is not only running out for Ionica customers, but for the operators as well. BT has 17,000 customers waiting to be connected, and the remaining 12,000 customers will need connecting by somebody in the next two weeks.
BT says it is confident it can complete all its connections in time.
"We see no problem in having these (connections) sorted out by the deadline," said a spokesman.
Latest Tesla news: Tesla stock price tanks amid reports of 'widening probe' by SEC and claims the base Model 3 loses money
SEC 'probe' takes its toll on Tesla as new research suggests that Tesla loses $6,000 on every $35,000 Model 3
10nm Cannon Lake Core i3-8121U CPUs make a rare outing with Intel's NUC mini PC
'Notorious' Australian child hacker thought he had executed 'flawless' hack
The former employee says that Tesla fired him for bringing the accusations to management internally