What options are there for sending notifications to iphone/android app/webapp?

I am developing a system where I wish messages to be sent to users iphone and android phones, without using sms. What are the different options I should consi开发者_开发技巧der?

APNS (Apple Push Notification Services) for iPhone, C2DM (Cloud 2 Device Messaging) for Android. There are also some third-party cross-platform push services available.

You can also turn the way around. The phones can poll if there are new things available on the server. Another option could be a http server push. Long Polling can also be used.