Temperature-sensing accelerometers are possible, but Japanese researchers at the Rekimoto Lab have taken it a step further with their AffectPhone project, which monitors Galvanic Skin Response for conveying emotions through an iPhone.
Sensors on the sides and back of the phone would allow the user holding the phone to feel heat or coolness depending on the emotions of the other person on the line. Both people having the conversation would need sensors on their phones, to measure the electrical resistance on one, and receive it on another.
A video below shows it in action, however as it's in Japanese you won't get much out of the demo admittedly. I'd recommend checking out Rekimoto Lab's [email protected] project video as well - it's the future for cat owners, I swear. [Rekimoto Lab via Recombu]