Hey there
I got kinda solution when having wifi issues with iOS6 on the iPhone 5!
When you did your backup via iCloud on your iPhone (not iPhone 5^^) and you restored (or want to restore) your backup on the new iPhone from the Cloud you may experience wifi issues!
The clue is, not to restore from the iCloud backup but the iTunes backup! When you do an iTunes backup and restore from that backup, you will have no wifi issues anymore!
Julian
I got kinda solution when having wifi issues with iOS6 on the iPhone 5!
When you did your backup via iCloud on your iPhone (not iPhone 5^^) and you restored (or want to restore) your backup on the new iPhone from the Cloud you may experience wifi issues!
The clue is, not to restore from the iCloud backup but the iTunes backup! When you do an iTunes backup and restore from that backup, you will have no wifi issues anymore!
Julian