The UK's mobile networks have begun shutting down their 3G services - which allow people to use the internet - in preparation for the rollout of 5G.
But Ofcom data show that 7% of Britain, virtually all of which is in the countryside, has no access to the 4G and 5G networks replacing 3G, reports The Telegraph.
Vodafone and EE are the first networks to have completed the full 3G switch-off across its network, with Three due to start this month and O2 to complete next year.
Countryside groups say people who live in rural areas are being left isolated and the switch-off will risk lives, with farmers potentially left without location services in an accident.
Official data show an extra 2% of the country will be thrown into a data blackspot by the 3G switch off, under current 4G coverage levels.
The networks and the regulator are facing calls to halt the switch off until 4G coverage is improved to avoid rural blackspots increasing.
Simon Gardner, sales manager of Stonehouse-based Lister Unified Communications, said: "I've already had some comments on social media about it affecting people and also affecting signal on trains when people are travelling. They've noticed a difference since the switch-off.
"For lots of people in the countryside, 3G was the only signal they had. What's supposed to happen is that they will reuse the frequencies to put in 4G and 5G and you will get a signal on the network.
"I suppose it's that old argument that when they bring the new network they always do the big cities and towns first and finally get round to some of the countryside but quite often its areas of the countryside that need it most. You fall over and break your leg in the middle of London and someone will notice, but if you fall over in the middle of Dartmoor you might not see anyone for days.
"Some people - a very small percentage, which tends to be the more elderly - have a phone in their car for an emergency and they tend to have the cheaper handsets which are 2G and 3G only so they need to upgrade and change their phone and maybe their SIM card and tariff to a more up-to-date version so they can pickup 4G and 5G.
"Some people have an old SIM card and an old tariff but have a 5G handset but to make 5G work you have to have the correct SIM card, the correct tariff and the correct phone."
Simon advised people to take advice from whoever supplies their SIM and tariff.
As for the business community, he said: "We've been getting lists for quite a while of customers we believe are using old handsets to try and pre-empt it. We've had customers in this situation but we've contacted them to advise them what they need to do.
"If you are a business you can come to us. We are selling lots of multi-network SIM cards. We've had a lot of business customers who have noticed a big change. I've got some who have been on the same network for decades but are now thinking about changing because it's really affected their ability to contact their people."
For businesses wanting advice and more information, contact Lister Unified Communications on 01453 829200, email hello@lister-communications.co.uk or visit lister-communications.co.uk