It's not clear what is going on. EARFCN refers to the LTE band (center) frequency. So the error implies that the phone isn't seeing a signal on LTE B3. Perhaps you are in a weak signal area or your phone may not be properly configured for LTE e.g. bad carrier config file, CSC not recognized, not unlocked, faulty radio alignment, carrier side issues. What does the *#0011# menu say about your LTE signal and what are your data speeds like?
It's a little surprising that the LTE app doesn't support your N3.. most Samsung phones including the S5 are supported. There are half a dozen similar apps though and one of the others will probably work for you. You should look into that, it will help you sort this out.
1800 Mhz (LTE band 3) is assigned to your carrier, so perhaps try it again in another locale. If you don't see an obvious cause for the issue you might want to try installing a different modem or open a support ticket with Mobitel.
ya I saw a comment also that telling not supported by N900T some user.
ya i have to try in another location, well if I install different modem is it cause to bootloop or something?? if it do is there any rescue method??
And need another big help, please give me a modem file of N9005 that can install and try on my phone??
And tell me how to backup current modem file??
I have rooted my phone but I haven't install any CWM or TWRP or any other kernel except original ones..
see image.. my current firmware and baseband..