iPhone 5 3G problems

Question

iPhone

Initial data:
iPhone 5 32gb A1428 iOS 6.1 (10B143) was brought from the USA, bought without a contract for full price.
Nano-sim of the MTS operator (Belarus), obtained at the MTS SC, i.e. not cut out of the micro-sim or standard.

Problem:
Quite often, the connection from 3G to EDGE and vice versa “jumps”. In 70% of such cases, this is followed by a complete lack of Internet connection with a fully working GSM connection. It goes away on its own after 1-2 minutes or after turning the airplane mode on and off. The phone has been in the same geographical location all this time, where everything worked stably a minute ago.
The iPhone 4 had a micro-sim with the same contract from MTS and everything worked without any complaints.

Can anyone come across this? What could be the reasons? Is there any way to fix this?
Thank you.

Answer 1

There is a discussion on w3bsit3-dns.com about this, they say that the cant is in the firmware. Yabble periodically releases fixes now very often, it makes sense to update the firmware. What is the current firmware?
Sorry, I saw the version.

Answer 2

Posted in the wrong thread.

Answer 3

I myself had problems with 3G after installing 6.1. After updating to 6.1.1 and later 6.1.2 there were no problems.