Does Android support near real time push notification?

Firebase Cloud Messaging FCM FAQ is the new version of GCM. It inherits GCM’s core infrastructure to deliver messages reliably on Android, iOS and Chrome. However they'll continue to support GCM because lot of developers are using GCM SDKs today to handle notifications, and client app upgrade takes time.

As of June 26, 2012, Google Cloud Messaging is the preferred way of sending messages to applications running on devices.

Previously (and now deprecated), the service was called Cloud To Device Messaging.

XMPP is a good solution. I have used it for a push enabled, realtime, Android application. XMPP is powerful, highly extensible and easy to integrate and use.

There are loads of free XMPP servers (though out of courtesy you shouldn't abuse them) and there are open source servers you can run on one of your own boxes. OpenFire is an excellent choice.

The library you want isn't Smack as noted above, it's aSmack. But note, this is a build environment - you will have to build the library.

This is a calculation I did on battery life impact of an XMPP solution:

The Android client must maintain a persistent TCP connection by waking up periodically to send a heartbeat to the XMPP server.
This clearly imposes a cost in terms of power usage. An estimate of this cost is provided below:

• Using a 1400mAh battery (as supplied in the Nexus One and HTC Desire)
• An idle device, connected to an 3G network, uses approximately 5mA
• The wake-up, heartbeat, sleep cycle occurs every 5 minutes, takes three seconds to complete and uses 300mA
• The cost in battery usage per hour is therefore:
  • 36 seconds 300mA = 3mAh sending heartbeat
  • 3600 seconds 5mA = 5mAh at idle
  • 4:95 + 3 = 7:95mAh combined
• A 1400mAh battery lasts approximately 11.6 days at idle and 7.3 days when running the application, which represents an approximate 37% reduction in battery life.
• However, a reduction in battery life of 37% represents the absolute worst case in practice given that devices are rarely completely idle.

I recently started playing with MQTT http://mqtt.org for Android as a way of doing what you're asking for (i.e. not SMS but data driven, almost immediate message delivery, scalable, not polling, etc.)

I have a blog post with background information on this in case it's helpful http://dalelane.co.uk/blog/?p=938

(Note: MQTT is an IBM technology, and I should point out that I work for IBM.)