There are a range of great articles and samples showing how MQTT can be used on the Android platform.
Android MQTT Push code sample for German Eclipse Magazin article on Eclipse Paho on Android
First Android Service from Ben Hardill
HelloMQTT a simple example
ListMQTT follow-on demonstrating listing by topic
Using MQTT with Android on IBM developerWorks (in Chinese)
Android-Paho-MQTT-Service - A simple MQTT Service that will keep running for the duration of your Android application using the Paho Java MQTT Client.
mqttitude - A Google Latitude replacement based on MQTT
There are also some good write-ups out there about reasons to use MQTT on mobile platforms:
MQTT Community Wiki by mqtt.org community members is licensed under a Creative Commons Attribution 4.0 International License and was made possible by the generosity of all of its contributors.