The move, supported by Oftel, the telecoms watchdog, would see BT relinquish the use of its brand name for local customers who take up the service, known as "Calls and Access".
Yesterday BT revealed the two companies which will take part in a technical trials of the package, which will run for three months.
They are Long Distance International (LDI), a US owned phone business which buys bulk capacity from big operators and sells it at cheap rates to consumers, and UniqueAir, a mobile business.
Homes which take up the offer will receive a bill from LDI or UniqueAir, despite being on the BT network. LDI has grown rapidly since its UK launch 18 months ago, by offering calls to the US for just 7 pence per minute. BT hopes the service could bring new business from potential telecoms operators such as banks or retailers.
However, doubts remain about the prices BT is charging for the service, which apparently give rival firms little room to make profits on top. Bill Noseworthy, LDI's managing director, said Oftel was investigating whether BT was intending to use the service to subsidise the rest of its network. He said: "Instead of the local network being a BT birthright it's an industry heritage, because the taxpayer has after all paid for it."