Since there are more and more needs for mobile internet, I got an idea about mobile router. I have placed many RB951 with USB LTE modem but it is not so mobile, it's big and it has to be plugged somewhere so my suggestion is to make a small router with integrated battery and LTE interface. Should have not more than 2 LANs and, of course, one USB port to plug the phone to charge the battery.
So, Android phone can't replace it 100% with functionality. Especially if we consider dataplan for mobile users. Mostly operators offer data card with special pricing which is not able to make phone calls.