Tavistock College and Primary School want to buy the large British Telecom building which stands next to their premises by the A386 Plymouth road.
The schools' heads, John Simes and Joe Flynn, Devon County Councillor Roy Cook and West Devon and Torridge MP John Burnett, met at the site last week.
But BT said this week that the premises are not yet for sale.
The building, a repeater station for boosting signals, was still in use and was connected by fibre optic cables to the Goonhilly Satellite Station in Cornwall, a BT spokesman said.
'To take it out of the network would cost more than £1-million. The school was told this after an engineering survey in the summer.'
However, Graham Stoate, assistant vice-principal at the college, said: 'We are dealing with the estate agents who have been engaged to sell the building by BT and we are beginning negotiations in good faith.'
Exeter estate agents Alder King have prepared details for a sale of the property, including a price of £150,000.
The collapse of the deal would greatly disappoint the schools. The building could serve the needs of both, as well as providing a new community centre.
The college wants more space for its sixth form and for in-service teacher training. At present, teachers have to travel to Exeter or Totnes for training.
The primary school needs a new assembly hall. Only around half of its 400 pupils can gather in its existing room, said Mr Flynn.
'It is the fifth largest primary school in the county and we badly need more space,' he said.
'The large room on the first floor of the BT building could accommodate them all at once.'
The town could benefit through a new centre for computer training and arts workshops, among other activities.
Shared use by the community could entitle the buyers to financial aid from the South West Regional Development Agency.
Mr Simes and Mr Flynn approached Mr Burnett a few weeks ago for help in acquiring the property.
Mr Burnett and Mr Cook have asked Devon County Education Department to make a bid for it and expect negotiations to start soon.
Mr Burnett said: 'I have written to BT's chairman Sir Ian Vallance saying that it is crucial for the Tavistock schools and the community to own this building.'
BT has a charitable arm, so it could be possible to reach an agreement which was not wholly on a commercial basis. The company has an interest in education, through its sponsorship of the Teaching Awards.
In a press statement to the Times, BT said it was assessing whether the building was a 'suitable target for disposal'.
It confirmed that property agents had drawn up preliminary particulars and that these had been given to the college. 'A number of people have been shown around the site,' said the statement.
Fred Eastman, of BT Property said: 'We are aware of the interest from Tavistock College and will be looking to discuss this issue with them once our position becomes clearer.
'At all stages we have attempted to ensure it is understood that — while we are looking at the viability of a future sale — the site is not currently on the market.
'We will endeavour to keep all interested parties fully informed.'
The building, believed to be about 50 years old, measures 9,000 square feet and has three floors and a basement.
It is in good condition externally, but a lot of work would need to be done internally to make it suitable for use by the schools and the community.
There are also garages and stores and a third of an acre of land which would need to be put in order.
Mr Simes said: 'I was told BT expected to remove its cabling in the second half of next year.'
Mr Cook said: 'It (the acquisition) could be a step towards gaining Learning Town status, which would entitle Tavistock to more funding from the European Union.'