Unfortunately, p2p is *inhales* fxxxed! due to how modern internet networks are set up. NAT (potentially VPNed at carrier level), lack of IPv6, firewalls blocking incoming traffic, dysfunctioning UPnP, blocked UDP. Next tier issues: legal, that bound user identities to IPs, showing your IP publically is a privacy risk first and a security risk second (DoS).

It seems like it'll be impossible without an overlay network (like Yggdrasil, i2p), but these will be too heavy for mobile devices without a dedicated functioning relay... here we go again.