iMessage problem with iOS 7 ?

Help, please. I downloaded iOS 7 yesterday on my iPhone 5, and now, all of my text messages with another iPhone 5 user (who also downloaded iOS 7) are coming through as SMS (green), rather than iMessage. In other words, I'm now eating against my monthly text allotment, rather than using iMessage at no charge. I checked Settings: iMessage is ON, Send as SMS is ON, and MMS and Group Messaging are ON. I have texted with other iPhone 5 users who have not yet downloaded iOS 7 and iMessage is working normally (blue messages). If it matters, I'm a Verizon user. I'm at a loss as to how to correct this problem. I don't think it's a Verizon problem, other than the fact that I'm rapidly going through my monthly text allotment. I've searched on the Apple site for a cure to this problem to no avail. (And today sure isn't the day to stop by my Apple store for some help.) Can anyone offer help? Thanks much in advance.

Try sending the iMessage to this user's email address rather than his phone number and let us know if that sends as an iMessage.

You might also try actually restarting your iPhone (a lot of people do not seem to be aware that sleeping ≠ powering down and restarting).

Thanks for the suggestion. All has been resolved. My friend had the iMessaging button turned off. Such a simple fix . . . it took us 4 days to figure it out.