Why Does 5G Stop Working When Dual SIM Is Enabled? 

First, an important correction: 

Dual SIM does not automatically disable 5G on modern phones. 

Current Pixel phones from the Pixel 4a (5G) onwards can connect to 5G while operating in Dual SIM mode.  

Modern iPhones support Dual SIM with 5G too. Apple notes that iPhone 12 models needed iOS 14.5 or later for 5G with Dual SIM.  

So if 5G disappears the moment you activate a second SIM, the problem is more likely to be which SIM is handling data, the handset’s software, network compatibility or what happens during calls. 

He Added an eSIM and Lost 5G 

Bilal had his normal UK SIM set up for calls and data. 

Before travelling, he added a second eSIM. 

A few minutes later, his phone showed 4G. 

Naturally, the new eSIM got blamed. 

After opening the SIM settings, he realised the phone had switched mobile data onto the second line. 

That plan didn’t have the same 5G setup in his location. 

He moved mobile data back to his UK SIM and 5G returned. 

Dual SIM wasn’t the problem. 

The phone had simply changed which SIM was doing the heavy lifting. 

Only One SIM Normally Handles Mobile Data 

This is probably the most important bit. 

Dual SIM lets two numbers remain active for calls and messages, but the phone generally uses one mobile data connection at a time. 

Apple says iPhone uses one cellular data network at a time.  

Google says the same basic thing for Pixel: only one SIM can be selected as the default data SIM.  

So before digging any deeper, check which line is selected for mobile data. 

That solves a surprising amount of Dual SIM drama. 

Calls Can Make Things Look Even Stranger 

This is where Dual SIM gets a bit fiddly. 

On iPhone, Apple says that if you’re on a voice call using a number that isn’t the designated data line, cellular data may not work during that call unless Allow Cellular Data Switching is enabled and the relevant network features are supported.  

Pixel phones have similar options around data during calls and automatic data switching.  

So you might see 5G normally, answer a call on SIM 2 and suddenly notice data behaving differently. 

Then the call ends and everything changes again. 

That doesn’t necessarily mean 5G is broken. 

Dual SIM is juggling two networks with one radio system and occasionally the juggling becomes visible. 

Older Phones Are More Likely to Be Awkward 

Dual SIM 5G support has improved dramatically. 

Google says Pixel 4a (5G) and later models can connect to 5G in Dual SIM mode.  

Apple specifically points out that iPhone 12 required iOS 14.5 or later for 5G while using Dual SIM.  

That means an older handset, old software or a strange carrier combination deserves suspicion before Dual SIM itself does. 

Update the phone before troubleshooting further. 

Yes, software updates are boring. 

They are still cheaper than buying another handset because one icon changed. 

Check the Right Settings 

On Android, open your SIM settings and confirm which line is selected under Mobile Data. 

Then open the network settings for that SIM and make sure 5G is allowed as the preferred network type where the option exists. 

On iPhone, go to: 

Settings > Cellular / Mobile Data > Cellular Data 

Choose the SIM you want handling data. 

If you want the phone to switch data lines during certain calls, review Allow Cellular Data Switching. 

Then toggle Airplane Mode once and let the phone reconnect. 

Do not delete both SIM profiles because somebody on a forum said that fixed theirs. 

We can troubleshoot without setting fire to the furniture. 

Where Talk Home Mobile Fits 

Talk Home Mobile currently supports 5G on compatible Android and iOS devices where 5G coverage is available. Its service guidance also says a compatible phone will automatically move between 5G and older available network technologies depending on coverage.  

If you’re using Talk Home Mobile as one line in a Dual SIM phone and want its 5G connection for data, make sure Talk Home is actually selected as the mobile-data SIM. 

Also check handset compatibility and keep the software updated. 

Dual SIM itself should not automatically prevent a modern supported handset from using 5G. 

Final Thoughts 

If enabling Dual SIM makes 5G disappear, don’t assume phones simply “can’t do 5G with two SIMs”. 

That advice is outdated for plenty of current devices. 

Start with the data line. 

Then check software, preferred network settings and what happens during calls. 

Most of the time, the second SIM hasn’t broken 5G. 

Your phone has simply started using the other line for something you weren’t expecting.