Martin Lewis is urging everyone with a mobile phone to check as soon as possible, because you might lose your service otherwise.
The money guru made an announcement on the latest edition of The Martin Lewis Money Show Live on ITV1, which was broadcast live from Liverpool for the last episode of the series.
Martin said that a change being made to mobile network signal is potentially going to affect many mobile phone customers and you might even need a new SIM card or phone.
Read More: Martin Lewis urges everyone with a payslip to check it now
The issue is that all the major networks in the UK - Three, O2, Vodafone and EE - and subsequently, sub-networks like Sky and Giffgaff - are getting rid of their 3G networks.
That means if you have an older phone, one which can only get 3G signal, you will lose internet access soon.
Some companies such as Vodafone have already begun switching off.
Martin is urging people to check their mobile phone's settings and make sure you can get a 4G or 5G signal. If you cannot, you may need a new phone very soon.
You can check if you have 4G or 5G by turning the phone's wifi off and checking for a 4G or 5G symbol. Otherwise, you can see in your phone's mobile networks settings what type of internet you have.
Martin Lewis told viewers: "Look, if you've got an old mobile handset, you may lose internet access soon.
"3G signals are starting to be switched off, Vodafone has already started in some areas, the others are doing it soon.
"Check on your phone setting that 4G or 5G is listed and enabled.
"If not, you'll likely need a new phone and in a few rare cases, a new SIM.
"There's not many out there but it's important to know."
It comes after Martin Lewis warned that an average 17% price rise is going to hit mobile phone customers from April.
Most networks are pushing prices up to account for inflation - which, ironically, will cause more inflation - but the money expert said that there are a few ways to challenge it.
If you're out of contract, and as many as 7 million customers in the UK are, you can ring up 'customer retentions' to negotiate a better deal, usually armed with knowledge of the best deals from comparison websites.
First, though, you should send two free texts to get the information to help your haggle - more on that plan of action here.
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