iPhone owners report of iMessage failures with iOS 7, simple procedure may be temporary fix
According to multiple reports on Apple's Support Communities webpage, iPhone owners who recently upgraded to iOS 7 are experiencing issues with iMessage, though a simple software reset may resolve the problem, at least temporarily.

A number of Apple's Support Communities users have reported an apparent iMessage bug that is causing messages to go unsent, unreceived or sent as a text on a variety of iPhones models running iOS 7. Others complain that iMessages are not being converted to SMS texts, as would be the case if Apple's servers were down, and are simply not being sent.
Some threads date back to Sept. 18, when Apple released the latest iOS to the public, though posts regarding the perceived issue have become increasingly frequent since the most recent iOS 7.0.2 update went live last week.
Support Communities forum members may have discovered a solution, however. Users are finding success with the following procedure: disable iMessage in Settings -> Messages, reset the iPhone's Network Settings under Settings -> General -> Reset, then reenable iMessage. The method was also reported to be successful by MacRumors on Monday.
There are variations on the method that include shutting down the handset for three to five minutes, though the technique has seen mixed results.
It is unclear how widespread the iMessage problem is, but one AppleInsider staff member can confirm their handset was affected by the issue. Employing the above network reset did work, however, and the iPhone remains stable as of this writing.
The purported iMessage troubles are the latest in a string of minor bugs users have reported following Apple's launch of iOS 7 less than two weeks ago. The company subsequently pushed out two updates, the first being a day-one patch that dealt with the iPhone 5s' Touch ID sensor, while the second squashed a lock screen passcode bypass bug.

A number of Apple's Support Communities users have reported an apparent iMessage bug that is causing messages to go unsent, unreceived or sent as a text on a variety of iPhones models running iOS 7. Others complain that iMessages are not being converted to SMS texts, as would be the case if Apple's servers were down, and are simply not being sent.
Some threads date back to Sept. 18, when Apple released the latest iOS to the public, though posts regarding the perceived issue have become increasingly frequent since the most recent iOS 7.0.2 update went live last week.
Support Communities forum members may have discovered a solution, however. Users are finding success with the following procedure: disable iMessage in Settings -> Messages, reset the iPhone's Network Settings under Settings -> General -> Reset, then reenable iMessage. The method was also reported to be successful by MacRumors on Monday.
There are variations on the method that include shutting down the handset for three to five minutes, though the technique has seen mixed results.
It is unclear how widespread the iMessage problem is, but one AppleInsider staff member can confirm their handset was affected by the issue. Employing the above network reset did work, however, and the iPhone remains stable as of this writing.
The purported iMessage troubles are the latest in a string of minor bugs users have reported following Apple's launch of iOS 7 less than two weeks ago. The company subsequently pushed out two updates, the first being a day-one patch that dealt with the iPhone 5s' Touch ID sensor, while the second squashed a lock screen passcode bypass bug.
Comments
This is one way it was fixed in the one iPhone that had the problem.
Siri has been very flaky since I updated. I use Siri quite a lot. I never used to get so many server error message or just being so unresponsive before. I don't get many iMessages as most of my texts are standard messages from devices other than iOS users so I am not sure if I am having any problems with that or not.
For this sort of trouble shooting I always try to get things work with the least 'amount of restrictions', meaning:
Disable MAC address filtering
Do not hide the SSID
Enable DHCP, do not use a static IP
Do not limit the DHCP lease time
Turn off all other WiFi devices in the vicinity
Hold iPhone in sight of AirPort, no concrete blocking of any kind
Configure a new WiFi password (nothing fancy as in special characters), try WPA2 first, but if this list doesn't fix it try all the other security options
Start AirPort from cold boot, wait for green light
Start iPhone from cold boot, give it time to find the WiFi signal
If that works one can add one security measure after the other, testing one by one. Add other WiFi devices. Test longer distances et cetera.
grrrr.
I get an error on my phone that the message wasnt sent. I am not receiving the messages on my iPad. The messages have started to appear on my MacBook Pro after not appearing right after upgrading both of my iOS devices.
For this sort of trouble shooting I always try to get things work with the least 'amount of restrictions', meaning:
Disable MAC address filtering
Do not hide the SSID
Enable DHCP, do not use a static IP
Do not limit the DHCP lease time
Turn off all other WiFi devices in the vicinity
Hold iPhone in sight of AirPort, no concrete blocking of any kind
Configure a new WiFi password (nothing fancy as in special characters), try WPA2 first, but if this list doesn't fix it try all the other security options
Start AirPort from cold boot, wait for green light
Start iPhone from cold boot, give it time to find the WiFi signal
If that works one can add one security measure after the other, testing one by one. Add other WiFi devices. Test longer distances et cetera.
Thanks. What puzzles me is...in my house, another iP5 and 3 iP4s ...all upgraded...and didn't have a problem. Why this one?
A simple reboot worked for me, my wife, and a coworker.
Careful. That's how Android users get by. Every. Hour.
Happily, I can report: no iOS 7 problems here--with iMessages or anything else (knock on wood). Except:
My iPad 2 was slow, stuttery, and even crashy for about an hour... and then it was fine. Go figure. I think some re-indexing or other memory-hoggage must happen for a while right after the update.
No problems at all on iPhone 5.
Wouldn't go back if I could!
(I also wouldn't rush to put it on an iPhone 4.)
Topical but off topic. I've NEVER had a problem in the past but since updating to iOS7 I cannot consistently connect my iPhone5 via wifi, and even when I do, there is a connection but no data throughput. I've tried all of the "try this" suggestions and I've even done a clean install to no avail. Any suggestions?
Install iOS 6.1.4? /s
I can confirm this fix solved the issue on my iPhone 5 running release version of iOS7 (no issues while using various beta versions). The problem surfaced 2 days ago and wouldn't go away. I was able to convert to SMS though. I re-activated the iMessage service, but had to reboot the iPhone to make any difference.
Messages>Send as SMS
which for me is off after the update. The description is, "Send as SMS when iMessage is unavailable".
Have experienced a strange aside to this issue. In recent days I got a string of iMessages and replies from a strange number in the UK - I am located in Ireland. I decided just to delete them rather than reply in case they contained some form of malware (not sure if my iPhone could be "infected' in this way. Anyway messages have ceased in last 48 hours.
My first issue ever with iPhone messaging since iPhone 3s.
Of course I messaging is a recent addition
This worked for me as well.
guess i lucky!