topic Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle in Other Galaxy S Series

Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

Members_GXqn1XH — Sun, 06 Jul 2025 19:20:52 GMT

Hi - i bought a Samsung S21 Ultra 5G (model SM-G998U1) it arrived complete with a dual SIM cradle. I have 2 x UK SIMS (both work when placed into SIM1 slot of the cradle). I check 'About Phone' it shows 2 x available IMEI numbers. I have reset network setttings, rebooted into safe mode - SIM2 does not show up here either. No matter what I do i cannot get SIM2 to recognise there is a SIM card in the SIM2 slot. I am up to date on software updates (current is on One UI version 7.0, Android 15, Baseband version G998U1UESGHYF1)

What is the problem with this please? I don't have eSIMs installed, the two physical SIMs both work in the S21 when placed into SIM1 slot, there seems to be a software issue that prevents recognition of the two SIMS being inserted together.

I was under the impression this phone could handle 2 x physical SIMs, but my handset cannot even see the two together?

Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

xSteveuk — Sun, 06 Jul 2025 19:37:26 GMT

How to use Duel Sim cards

https://www.samsung.com/uk/support/mobile-devices/how-to-use-or-manage-dual-sim-cards/

Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

Members_GXqn1XH — Sun, 06 Jul 2025 19:57:29 GMT

Hi - thank you I checked the link to be sure i hadn't missed anything but its the same - SIM2 is not showing up. All i see is SIM1 (UK Mobile carrier) switched to 'on', then beneath that is 'eSIMs' and option to add eSIM. No SIM2 is detected. Is this a software issue in that the option may not be enabled on my model of phone at all or there is a firmware/update for the phone i'm missing please? Thank you for your help.

Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

xSteveuk — Sun, 06 Jul 2025 20:04:10 GMT

First
Are you sure your phone is duel sim supported

Is the sim in the slot correctly

Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

ynneL — Sun, 06 Jul 2025 20:22:18 GMT

G998U1 appears to be an unlocked USA version of the S21 Ultra so all I can think of is maybe it's a software restriction with that specific model

Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

Members_GXqn1XH — Sun, 06 Jul 2025 20:22:28 GMT

When you ask if phone is dual sim supported - its a Galaxy S21 Ultra 5g - manufacturer says its dual-sim enabled and others on the community can use the phone in this way.

SIM in both slots seated correctly (tried and reseated several times in alternating combinations) - only ever recognises SIM1 - never SIM2

Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

Members_GXqn1XH — Sun, 06 Jul 2025 20:23:18 GMT

Also i just checked and the setting 'Dual SIM always on' is greyed out completely ?

Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

xSteveuk — Sun, 06 Jul 2025 20:27:32 GMT

If your Samsung phone's dual SIM options are greyed out, it usually indicates a problem with SIM card detection or a software glitch. You can try troubleshooting by checking SIM card placement, restarting your phone, or resetting mobile network settings. If the issue persists, consider contacting Samsung support or a repair shop.

Here's a more detailed breakdown:

1. Check SIM Card and Tray:

Ensure both SIM cards are properly inserted into their respective slots.

Remove the SIM card tray and reinsert it, making sure it's fully seated.

Try swapping the SIM cards to see if the issue follows a specific SIM.

2. Restart Your Phone:

A simple restart can resolve temporary software glitches that may be affecting dual SIM functionality.

3. Reset Mobile Network Settings:

Go to Settings > Connections > SIM card manager > More SIM settings and look for an option to reset or manage mobile network settings.

Be aware that this will reset saved Wi-Fi networks and passwords.

4. Check for Software Updates:

Outdated software can sometimes cause dual SIM issues. Check for available updates in Settings > Software update > Download and install.

5. Dual SIM Always On:

If you're trying to use "Dual SIM Always On," ensure it's not greyed out. You may need to set a preferred SIM for calls and messages first.

Navigate to Settings > Connections > SIM card manager > Preferred SIM card.

6. Safe Mode and Factory Reset:

If the issue persists, try booting your phone in Safe mode (which disables third-party apps) to see if the problem is app-related.

If Safe mode doesn't help, a factory reset (after backing up your data) might be necessary.

7. Contact Support or Repair:

If none of the above steps work, contact Samsung support or a reputable repair shop

Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

Members_GXqn1XH — Sun, 06 Jul 2025 20:33:35 GMT

Hi thank you and USA? Thats strange as i bought it refurbished from Giffgaff (legit UK dealer on refurbed phones here) so unsure why its a USA version - guessing someone else traded it after buying in the US then. Is there anything that can be done to undo the restriction do you think?

Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

Members_GXqn1XH — Sun, 06 Jul 2025 20:36:34 GMT

OK thanks - i think reading down the list i've done a lot of these after reading other threads. Factory reset does sound a bit drastic but i might each out to support (its out of warranty of course now though). I have a feeling i might need to trade this in if this becomes an issue, or alternatively settle for an eSIM MVNO carrier. OK thanks guys very helpful with the ideas and thoughts. I'll check out support.

Re: Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

ynneL — Sun, 06 Jul 2025 20:44:19 GMT

According to this the G998B is the international model and the G998B/DS is the duel sim version I'm afraid I'm not sure if you can bypass software restrictions

Re: Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

Members_GXqn1XH — Sun, 06 Jul 2025 20:48:28 GMT

Hi ok thanks for checking for me. Appreciate the time spent.

Re: Re: Re: Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

NawtyRobot — Mon, 07 Jul 2025 02:30:59 GMT

Not all US phones are dual sim.

This was something my friend and I noticed years ago. I think they have chnaged it now but they were single sim phones for a long time. My friend lives in NY
I assume you couldn't find sim manager too?

Re: Samsung S21 Ultra 5G will not recognise SIM2 in dual-sim cradle

EddieMunster — Mon, 14 Jul 2025 01:35:38 GMT

I'm using an American S21 i got off ebay with mobile deals. I recently used a flash drive to transfer data from phone to laptop and now my Sim card isn't being recognized, I've gone into Sim manager, deleted 2 edits and then phone recognized Sim for about 1 minute, it started to not recognized Sim 1 minute after so I know something else has gone wrong. Would a bug in the flash drive have caused this or is it something else and can I fix it myself or do I need a repair shop ??