Should my text messages be blue instead of green after the iOS 5 update?

Blue messages are iMessages. Dont worry they work pretty much the same as txts

Instead of being sent via the sms service through your operator they're sent either as cellular data or wifi if you have it. The idea being that it functions in much the same way as BBM does on a Blackberry.

You can IIRC turn them off.

iOS 5 automatically determines if the intended recipient is using iOS5, and if they are, automatically sends the message as an iMessage rather than a txt. The colour change is designed to let you know whats what.

Blue messages = iMessage, which are messages sent between iOS 5 devices over Apple's servers

Green messages = regular text messages sent via your cell service provider, and which count against your plan limits (if any) for messaging.

Whenever your iPhone is showing blue text messages, it means that the message was sent to another iPhone using iMessage. Basically, it sends an instant message over 3G or WiFi, rather than SMS through your carrier. Whenever you send a message to another iPhone using iOS 5, the Message app will automatically try to use iMessage.

I have an AT&T iPhone 3Gs and am having no trouble sending/receiving blue texts within iMessaging with others on iPhones... except for my friend who just got a new iPhone 4 from Sprint. The texts he sends/recieves to/from me are still always green, even with his wife who also got a new iPhone 4 from Sprint. I don't think he's seen any blue messages yet. He just bought the phones after iOS5 had been released and I compared the software versions to see that we were running the same version. Why would his phone not be using blue messaging instead of green?

Did he check his settings -> Messages and make sure iMessage is actually enabled? And under General -> Restrictions (Allow:) does he have Facetime set to "on"?

K but why would the color just all of a sudden change? Could the person I sent the message to have gotten a new iPhone and that's why the color changed?

Yes, or they updated their iphone 3gs or 4 to ios 5. Also, they could have updated their ipad or ipod touch to ios 5, and are now using that for texting, although it probably would have given them a new number...idk how that works, as i only have a 3gs.