Need advice on type of server I should use

Hey guys, I've been messing around with unity for 4 years now and I am ready to create my first multiplayer game but I need some advice on what type of server I should use. Let me explain

The game is built for android devices, one time purchase (no in game purchases), max number of players in a game is 5, there will be no need to store information of these players like points,level ect... no information will need to remain after their game session closes.
All I need to gather from these players is location in the map and VOIP so they can't speak to each other.

I am trying to stay away from paid services as I don't believe the game will generate enough money to sustain it.

Is it possible to have the client be the host where they can simply invite other "known" players to join? Again for android (would like to cross with ios at some point). I have done this before on pc of course but never touched online/android yet. Also, if this requires users to use WIFI then that will be fine, but of course would like them to be able to play on 3G and 4G if possible.

If it is possible to go this route, then how can I have other users find specific people (in all cases it will be someone they know) who also own the game since there will be no dedicated server storing their information?
I am stumped with that one ^



I really would love some input here, any advice is seriously appreciated, I really want to start on the right foot with this project.

Thank you