Hmm.. I've just seen this happen. The answer is that, after 5 minutes, if the iMessage has not been delivered it auto falls back to SMS.

You can opt to 'Send as SMS' before that by clicking on the undelivered iMessage if you're in a rush.

Edited by xela (Tue 18-Oct-11 09:24:02)

Related question. I use an iPod touch when I send my daughter a message on her iPhone and she's not on the internet i.e. it goes via 3g, you pays for the message?

Because you're sending the message from an iPod, there is no SMS fall back.

Therefore, to receive the message, she needs an internet connection.

That can be WiFi, 3G, GPRS, whatever. If she's not on WiFi, when she receives the message it will use her mobile data allowance but a) messages are tiny in terms of data size and b) most iPhone tariffs include a data allowance.

So, short answer : it won't cost you anything, it shouldn't cost her anything

Thanks that's cleared things up.

When I message my daughter most of the time the imessage sits for 5 minutes, as described, then eventually sends as an sms. My question is why is it not going through as an imessage because she's either on wifi or 3G. In that case shouldn't the imessage always go through?