Hi everyone!
Is it possible to connect mobile phone to 3g gsm router for calling and data (admitting that gsm signal is too weak for mobile phone to use it so a gsm router with external antenna is neded). Mainly I'd like to know what kind of router and anything else is necessary. Thanks

 

You can certainly use your 3G sim card in one of the many small routers about, such as:
https://www.aliexpress.com/wholesal...B_20191225035526&SearchText=huawei+router+sim

But these may suffer from the same problem, although some of them have small RF connectors, that you can connect to an additional areal or booster, and I am not aware if can then make normal telephone calls as well.

You could consider a 3G booster itself like:
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20191225035727&SearchText=3G+booster