Messaging APIs for iPhone and Android

What are good APIs/services for offer开发者_高级运维ing in-app notifications for Android and iOS devices?

We need to send notifications in real-time. The notifications need to get sent independent of whether the user has the app open at the time.

Should we build from scratch or outsource?

Thanks!

iOS offers PUSH notifications, which you send through Apple's servers. They have a quick reference here: http://support.apple.com/kb/HT3576

If you want your service to run on older versions of android (pre-2.2) you probably need to develop something from scratch (I would derive something from XMPP), but Android 2.2+ offers something called C2DM (Cloud to Device Messaging) which is quite useful.