networking - What do you use to support multiplayer turn-based network game for iOS and Android games?

If I'm doing a turn-based card game, what kind of technique do you use to support multiplayer gameplay over Internet?

Is it socket? If it's socket, which SDK (CoronaSDK etc.) can provide solid socket library?

Can Unity3D can be used solely to support what I need without using other socket servers like SmartFox or Electro?