UPDATE It appears I might have been too hard a judge: having just sent an iMessage, iPhone was unable to deliver it for a few minutes, then automatically sent it as SMS.
The roaming problem with iMessage
The roaming problem with iMessage
The roaming problem with iMessage
UPDATE It appears I might have been too hard a judge: having just sent an iMessage, iPhone was unable to deliver it for a few minutes, then automatically sent it as SMS.