Iphone 4S does not catch the network without voice roaming enabled, what could be the problem?

Question

iPhone

Prehistory:
I bought the above device from the hands of a friend. I know that he is a neat user and did not hand it over for repairs. I inserted a Megafon SIM card, and then the problems began.
Device configuration:
Phone: Iphone 4S
OS: IOS 8.0.2(12A405)
Operator: Spirnt 17.0
Model: MD378LL/A
Problems:
1. If you turn off the roaming function, it does not catch the network, although everything works fine on another phone
2. Does not send SMS . The same problem was on the previous Samsung brand device, I called the operators and they tweaked something and arranged for me to send messages. On Apple, such a focus did not work, they say that the problem is in my device.
3. Does not want to work on the mobile Internet.
What I did:
1. I called the operator, they checked all the settings with him. As it turned out, everything is fine with the settings, there are no communication restrictions.
2. Changed the SIM card. No effect.
3. Worn in the service. They said that the device is in good condition and works fine.
4. Checked IMEI, everything is normal, the device is legal.
What I didn’t do, but I will definitely do it:
1. I haven’t tried SIM cards from other operators. If it helps to tear the Megaphone to pieces.
Question:
1. How to make cellular communication work in normal mode?
2. How to send SMS?
3. How to make it work on the mobile Internet?
PS: Please do not write about various hacks, jails and R-Sim, this option is not interesting to me.
PSS: Googled, maybe not too well, so please don't swear.

Answer 1

I just found out the following yesterday ... The phone turned out to be locked under Sprint, and there is no way to unlock it. Thanks to all.

Answer 2

It is logical to insert another SIM card and chat with a friend about the problem.

Answer 3

Maybe the new ios is not friendly with your SIM card?