Dual SIM phone limitations

Roger1

eDicky wrote: »

When you are using SIM 1 (O2) for mobile data, do you have any signal on SIM 2 (Three) for calls/texts?

My default is SIM2 (Three) for calls and data. Full signal for O2 (SIM1), 50+% for Three.

When I change mobile data preference to SIM1, I get full signal for SIM1, nothing for SIM2.

Full data signal either way.

But switching back to Three default, I get EMERGENCY CALLS ONLY on standby. This disappears when I switch on and I can make calls on both.

eDicky

Roger1 wrote: »

When I change mobile data preference to SIM1, I get full signal for SIM1, nothing for SIM2.

This indicates that the SIM not being used for data is limited to 2G, you cannot have 3G/4G reception on both SIMs at the same time. (Three network will not work on 2G in the UK.) This is the common limitation of dual-SIM phones that the thread is about.

Roger1

Thanks, eDicky

Roger1 wrote: »

But switching back to Three default, I get EMERGENCY CALLS ONLY on standby. This disappears when I switch on and I can make calls on both.

Seems to have been temporary. Not there now.

d123

Roger1 wrote: »

My default is SIM2 (Three) for calls and data. Full signal for O2 (SIM1), 50+% for Three.

When I change mobile data preference to SIM1, I get full signal for SIM1, nothing for SIM2.

Full data signal either way.

But switching back to Three default, I get EMERGENCY CALLS ONLY on standby. This disappears when I switch on and I can make calls on both.

Just be aware that when your data is set to sim 1 (your o2) then your sim 2 is effectively deactivated and you won’t receive calls/texts on the 3 sim. Using a 3 sim in a dual sim phone that only has 2G on the second sim means you’ve effectively just got a safe place to store the sim, not an actual sim in use.

Roger1

eDicky wrote: »

This indicates that the SIM not being used for data is limited to 2G, you cannot have 3G/4G reception on both SIMs at the same time. (Three network will not work on 2G in the UK.) This is the common limitation of dual-SIM phones that the thread is about.

d123 wrote: »

Just be aware that when your data is set to sim 1 (your o2) then your sim 2 is effectively deactivated and you won’t receive calls/texts on the 3 sim. Using a 3 sim in a dual sim phone that only has 2G on the second sim means you’ve effectively just got a safe place to store the sim, not an actual sim in use.

Thanks, both. I think I understand, but what I don't get is the screen showing 4G reception for the SIM in slot 2 (Three). That's when it is the preferred SIM for calls and data. Most advice is that dual-SIM phones only operate on 2G on the second SIM, and as you point out, Three don't offer 2G service. But I can make calls on Three.

Varying the SIM preferences, I find when SIM 1 is selected for data and SIM 2 for calls, I get 'network not available' when trying to make a call. Selecting SIM 1 for both, I can make calls.

Sorry to go on ... The reason this is important for me is that I'm using a roaming SIM for certain foreign travel where Three Like Home doesn't apply, e.g. South Africa. This SIM was originally intended for the second slot, but because of the 2G advice, I put it in the SIM 1 slot with my regular Three SIM in slot 2, which works well when it is the preferred SIM.

So I think I'm all set: SIM 2 for most purposes, SIM 1 when roaming in certain countries.

BTW the roaming SIM is from https://www.swiss.com/ch/en/book/swiss-choice/swiss-mobile
Many roaming rates CHF 0.14/minute, free to receive. South Africa to UK CHF 0.25/minute, receiving in SA CHF 0.11/minute.

d123

Roger1 wrote: »

Thanks, both. I think I understand, but what I don't get is the screen showing 4G reception for the SIM in slot 2 (Three). That's when it is the preferred SIM for calls and data. Most advice is that dual-SIM phones only operate on 2G on the second SIM, and as you point out, Three don't offer 2G service. But I can make calls on Three.

Varying the SIM preferences, I find when SIM 1 is selected for data and SIM 2 for calls, I get 'network not available' when trying to make a call. Selecting SIM 1 for both, I can make calls.

Think of it was Sim 1 (the sim active for data) and sim 2 (the sim not data active). If you set your Three sim as sim 2 you are effectively just deactivating it as the sim cannot work with a 2G signal.

This restriction may actually not necessarily be true when roaming, Three will have roaming agreements with networks that have 2G service.

But in the UK any dual sim phone with only 2G on the non-data active sim is useless if the second sim is a 3UK one.

Roger1

Thanks, d123. Much clearer!

I'll leave as is.

eDicky

Roger1 wrote: »

Most advice is that dual-SIM phones only operate on 2G on the second SIM,

The 'second SIM' is not necessarily SIM 2, it means the SIM that you are not using for mobile data.

Putting your Three SIM in either SIM 1 or SIM 2 will make no difference, it will not work (in UK) if that SIM is not selected for using mobile data.

This limitation will only affect you when using 3UK in the UK, and with any SIM in countries where 2G networks are not available.