You don't have to go back to IO to get the CoR. Like I said, once you've requested for a CoR by going to IO (one time), they'll send it to you by EMS. It takes about a week or two for it to arrive at your address.
If your phone isn't locked, manually select your network from Settings as opposed to letting your phone automatically find and select a carrier. You'll find instructions on how to do that on Google.
Ah, I see. I didn't know about that. In my case then, I'd ask the landlord to only file TM30 a few days before I go for 90 day reporting so my permanent address is what they have on the system when I go.
I don't wish to hijack this thread, but I have a related question: can we use a Thai driving license to check into a hotel? This way perhaps we won't need to file TM30 again when we return to our permanent accommodation.
Hence I mentioned visiting the immigration office to cancel the current stamp and get a new stamp for your preferred visa. You can have two valid Thai visas on your passport, but you can only be stamped for one of those visas at a time.