Iphone 4s wont receive text message in roaming, since i got and setup ipad.

I have ipad 3g+wifi, but not using it with sim card. Therefore, when i am in roaming, i cannot receive regular text messages on iphone 4s.

before i got an ipad, i was able to receive text messages (sms) while roaming.

Can anyone please help me? What did I do wrong?