Iphone texting other iphone user, no ichat?

I have 3G and my ichat is on. When texting other people with iphones my ichat works and appears as blue. But, I was texting a friend and all my texts are being sent as regular text messages. We text all the time and usually ichat always works. I know my phone is fine. He is travelling, so does it mean his ichat is off?

IMESSAGE!

Yeah he probably has his 3G turned

Yes.tell them to check the setting.general.messages and see if imessage is on