When I still had verizon, i had upgraded to a razr, but I still got texts on my iphone...well now I have tmobile and it's STILL happening.
I've only had tmo for a couple days, so it's possible my number hasn't completely ported over yet, but i miss half my texts cause they got to my iphone.
i DO have airplane mode on and when i see i've received a text, i go to open it and i get a pop up that says "can't send or receive messages while in airplane mode". oh ok then.
Are you sure these are good old fashioned text's rather than imessage? if they are imessage I'm not sure how you make sure apples servers know you are not on the iphone anymore.
If they are good old fashioned texts you really need to speak to your carrier