This might be usable if the devices are connected via wlan and both sides may configure routers and their firewalls easily.

Actually the multiple problems to get the real IPs and to circumvent the firewall, that mobile carriers use to actually protect you from your bad secured and configured phone, may provide a larger problem than the easy, but time consuming Q&A here.

Nevertheless: There might be ways to get around that, like there is reverse ssh to use ssh around a blocked port 22 by mobile providers