Google has released news of the Android Open Accessory Kit which will enable users to interact with external sensors and outputs from an Android phone using a development board based on the Arduino Mega2560. The kit will be priced around $400 but it will be possible to work with a much cheaper Arduino Host Shield and a standard Arduino.
It would be neat if a phone came out which had a row of programmable ports ready like the Arduino :). You could get instant texting support for turning on light/heat/etc. at home. Or the other way around - you would be able to have the phone monitor and report from any kind of sensor.