IPhones service being off and Wi-Fi/imessages?

1. My boyfriend is in Japan at the moment
2. He told me his phone would be off for about 2 weeks but he would be able to get and reply to messages only when connected to wi-fi
3. My imessages are saying delivered yet I'm not getting anything back from him at all

Is he lying or is something going on so that he's still not receiving messages? I was thinking that since he is overseas its some other issue he may have with the carrier but I thought imessage would work regardless?

They say 'delivered' but that does not mean they are 'received' and it means he hasn't read them. Don't worry about it. I'm sure he'll get back to you soon.