Mobile Networking questions

Hello,
I am new to mobile networking between users of the same app on x number of devices.
If I am creating an app that requires users and groups with users in it that can send & receive messages/small notifications from other users if online or if offline prompt them when they login that they have pending messages, what is the best way to design this? I read a lot about gamecenter for user authentication and multi-user, but it seems to be for games that have achievements and leaderboards, not necessarily multi user apps that are not games. Should I branch and create my own server & database? Seems like a lot of work for simple short messages to and from users in a particular group.
thanks

You guess it right buddy, there is lot of work for this small messaging app. You need to have you concepts clear.

For an example check Whatsapp and hike, these apps will give you bit of idea how things will work. But do not create just copy of these apps, you must have a unique and engaging idea.

All the best.