The upcoming 4G mobile auction should be used as an opportunity to upgrade the UK's mobile infrastructure, says an advisory group.
The Communications Consumer Panel said regulator Ofcom should oblige operators to extend services to rural areas.
It also suggested the money made by selling off the airwaves could be used to upgrade rural coverage.
It estimates that three million people live in mobile "not-spots".
The panel said it did not believe that new 4G services would extend beyond existing coverage.
4G is the next-generation for mobile services, offering faster speeds, crucial as more people use smartphones to surf the web.
The panel is suggesting that Ofcom run a "reverse auction" after the initial sell-off, in which operators can bid for money to extend their services in rural areas.
The 4G auctions begin next year with services likely to start rolling out from 2013.
There is a great deal of interest in the spectrum - which has been freed because of the switch to digital TV - as it operates in the low frequency 800MHz band.
This spectrum will be particularly good at penetrating buildings and will allow operators to offer better in-building coverage which is becoming an increasing problem as people use their smartphones at home.
The money freed up by the 4G auctions must be ploughed back into notspots, said the panel.
HOW TO BE A PART OF THE UK MOBILE MAP
- You will need an Android handset
- Download the app below or from Android Marketplace
- Once downloaded, data will be collected without you having to do anything more
- If you wish to see what coverage is like in a particular place, simply click on the app
- The app is free to download
- It uses very little bandwidth
- The data is anonymised and neither Epitiro nor the BBC will collate or store any personal data
It estimates that the UK needs an extra 1,400 base stations to improve rural coverage.
"This is a critical moment, and we have a unique opportunity to resolve the persistent problem of inadequate mobile coverage," said panel chair Bob Warner.
"Most places that were mobile coverage notspots 10 years ago are still notspots today, and the spectrum auction represents perhaps the only chance we have in the next decade to improve coverage in the nations and for rural communities," he added.
The BBC is conducting its own survey into notspots using an app developed by network analysis firm Epitiro.
Ofcom has said that mobile coverage is one of its priorities and is conducting its own research into the problem.
One of the biggest blackspots for mobile coverage is on rail networks.
Research conducted for Ofcom last year found that on the East Coast mainline the probability of maintaining a 15 minute phone call was as low as 10% for two operators.