As already explained above, the core network IP subsystem is the same on mobile as PC / console. If you can find the IP address of a server you can connect to it (any NAT punch through and firewall issues aside).
Blueprints - you are probably gonna have a bad time (not an expert).
-
What you are talking about is ‘presence sessions’ (finding friends via external services) in UE4 terminology. The UE4 back end implementations were very sparse last time I looked. There is another issue here - are you talking peer to peer or do you have a dedicated server living somewhere on the Internet. Commercial products often roll their own platform agnostic match making system.
-
As per @thejamsh I have Android working across local wifi via the OnlineSubSytemNull (LAN beacon - same subnet). At the time, I believe I had to fix a bug in the engine source to get this running as server (was a while back 4.6? and may already be fixed in 4.10).
-
Real time game Networking (not peripherals) via Bluetooth. Not there at present and probably not likely in the near future. UE4 runs on IP networking. In theory you could create an IP transport layer on top of an existing channel between two Bluetooth paired devices - there are various ‘share your Internet via Bluetooth’ apps around. Not sure how you would pair devices from within your app (API security concern restrictions).
While I can’t speak for Epic, I suspect they are developing ‘bang for buck’ features first. A feature for match making on a particular platform/service probably isn’t a very big priority for them (eg. 4.10 github now has splash screens on Android ‘out of the box’ - 19 months after the first release).