You all probably know it takes some effort to write an email from a blackberry or even more an iPhone. Most people do not expect you to write a long message if your are in a mobile situation and usually they know that with the final email signature appearing at the end of a message "Sent from iPhone/ Sent from Blackberry"
So here is a way to impress your friends. From your computer, write a long email. Just add "Sent from iPhone". Since there is no way to know if was sent from your computer, your friend will assume you took time to write a long message away from your computer. If you want to impress them even more, answer fast with a long answer to an email you just received with the same signature. You might not get a reaction from him immediately, but i can tell you it has a good effect on them. I am talking by experience.
Yes, i know this is stupid.
Btw you can also use this trick to AVOID long answers from your computer. People will understand :)