I've tried following smcclay's instructions a few times, and after a few tries I finally got it to work!
I don't have a second WIND sim card however, the only other card I have access to is from Speakout (7-11, using Rogers network).
I think the problem on my first two attempts was that after decoding the message from the +44 address and preparing my own SMS message, it took me about 60 - 90 minutes to get set up with a platform that let me send AT commands to a GSM device.
In that time, I think either my phone must have sent a second request to Apple, or maybe I inadvertently did it myself. I saw this message in the Baseband log after it received my attempt:
6348.727 sms: Rejecting PNR response: Received cookie that does not match one we created: 5df95244 != d744bfb
So with everything all plugged in and set up and ready to go, I repeated the whole process in the space of a few minutes:
- toggled imessage off then on again
- waited 15 or 20 seconds
- dumped the baseband log
- synced with itunes
- opened the baseband log and found the message from +44
- went through smcclay's instructions to recreate the new message
- sent the new message immediately
To verify, after 15 or 20 seconds I dumped the baseband log again and found the PNR success message. And sure enough, now my WIND phone number shows up as valid and working on iMessage.
YAY! So you do not need to use a second WIND sim card to do this; the Speakout / Rogers one worked. Also, for what its worth I don't have a phone that can do AT commands, I used a GSM shield and an Arduino.
And a big thank-you to smcclay for figuring all this out!
Cheers!