Second SIM slot on Lumia 950/XL supports only 2G service

This thread is about previous models just like what Abi99 (2) mentioned. Both SIM slots of the Lumia 950XL supports 2G, 3G, and 4G/LTE. You are creating an issue that doesn't exist.

This issue very much exists.

Case in point, it is now 2017, AT&T has shut down all their 2G towers and now my Lumia 950 cannot see any AT&T network on the second SIM.  If I disable the first SIM it works, gets 4g,  if I have both on and move data to the 2nd, it kills the connection and network for the first.  If I set roaming, nothing.

It appears there is a limitation where it will only do 2G on the SIM that is not doing data. It does NOT allow 3G or 4G.  Since neither slot is "set" for a speed, IO would hope this is a software issue and not a hardware issue.

Abi99 writes*:"Because this 4G/3G-for-one-SIM-and-2G-for-the-Other is a hardware limitation of the chipset"*

That ist false! The Lumia 950XL uses the Snapdragon 810 soc.

According to the manufacturer (qualcomm) this chipset

supports Multi SIM in this way:

• LTE Dual SIM Dual Active
• LTE Dual SIM Dual Standby

https://www.qualcomm.com/products/snapdragon/processors/810

The Snapdragon 810 soc even supports 450 mbps in DL peak!

Therefor it is Microsoft's fault if the 950XL implements LTE on both sim slots

in a mutually exclusive way. The Snapdragon 810 would allow support

for LTE on both sim slots simultaneously.

According to the developer description, Windows 10 mobile (like Windows Phone 8.1)

supports independent access to each sim (uicc) for all cellular related tasks:

https://msdn.microsoft.com/en-us/windows/hardware/drivers/network/dual-sim

Windows Mobile does support Dual Active however one line must be GSM.

But that is just one of Microsoft's weird design decisions that resctrict capabilities.

The situation in the 950XL is even worse because the implementation in the 950XL

is not "Dual Sim Dual Active".... it is "Dual SIM Dual Standby":

https://www.microsoft.com/en/mobile/phone/lumia950-xl-dual-sim/specifications/

So the 950XL has only one(!) tranceiver. Therefor only one sim can be active at a time.

Both slots support LTE but only one at a time. If slot 1 is LTE then slot 2 defaults to 2G and vice versa.

Johnathan, Microsoft does not leverage Microsoft Answers as feedback channel. Why ever. Therefore here, your feedback drowns in the Internet swarm. Because this 4G/3G-for-one-SIM-and-2G-for-the-Other is a hardware limitation of the chipset, there is nothing, which can be done except giving back your phone (or switch the data SIM). However, when it comes to Wi-Fi Calling with T-Mobile USA, please, let us continue in your previous thread…

If your SIM2 does not have any reception, you are able to change the data SIM.

However, I doubt this is what you are looking for.