Telstra plans to switch off its CDMA mobile network covering rural and regional areas and replace it in 2008 with a national 3G (third generation) service.
There are fears Telstra's 1.4 million customers will have to fork out for an expensive new 3G mobile phone once the CDMA service is switched off.
Mr Fischer, who fought for the introduction of CDMA in 2000, said an independent inquiry was needed to investigate Telstra's proposals.
"Given the fact there was public money in the CDMA mobile freeway ... these are matters that should be subject of an independent inquiry, especially with regard to footprint of services," he said.
"I think `not so fast, Sol' and not until there has been a proper comparison between CDMA and the new low frequency GSM (global system for mobiles) that (Telstra chief executive) Sol (Trujillo) is proposing."
Telstra says there is no need for an investigation because it has already made a commitment not to switch off the CDMA network until the new 3G service has the same sort of coverage in country areas.
"This isn't like back in 2000, when I think at the time Mr Fischer was deputy prime minister and the government switched off the analogue network causing some inconvenience to people in regional Australia," company spokesman Rod Bruem said.
"Telstra has given every undertaking that it will work with its customers on the transition and make it as easy as possible.
"We certainly don't want a repeat of what occurred back in 2000."
About $100 million of taxpayers' money has been invested in Telstra's CDMA network.
But Mr Bruem said the money had not been a waste even though the CDMA network would be replaced.
"Taxpayers should feel assured that 80 per cent of what's been invested through commonwealth programs will go into the new network," he said.
Meanwhile, Labor is preparing to unveil its new telecommunications policy this week, with a plan to roll out high speed broadband services as its centrepiece.
Opposition communications spokesman Stephen Conroy said Australia deserved to have a "true" broadband network, which was about 50 times faster than existing services.
He called on the government to help telecommunications companies roll out optical fibre broadband networks so there could be competition with Telstra's services.
Labor's plan calls for new laws to be drawn up to help joint venture companies build optical fibre infrastructure.
The joint ventures would maintain ownership and control of the network and would be banned from engaging in retail competition.
Instead, they would provide wholesale services to joint venture partners and access to outside third parties.
"This structural separation would destroy any incentive that the owners of monopoly infrastructure may have to discriminate anti-competitively in providing access to its infrastructure, reducing the need for continuing heavy-handed government intervention," Senator Conroy said.