This is what I posted after I tried doing it though AT&T last year -
Well... I can confirm that it can't be done through AT&T. I went to my local AT&T store today and thought everything was going to be good. The person that I talked to said that there was a way to do it. He swapped the numbers between the devices, activated the phone but couldn't activate the iPad. He tried it a few ways with no success. After that failed he suggested that I call AT&T because they can do more than a store can so I did that. Again, it got close and I thought it was going to work but no luck. The rep told me that it could be done if I was swapping the plan to another phone but it can't be swapped to an iPad. So... everything pretty much went back to normal.
But, I was able increase my data plan from 3GB to 5GB for an extra $8.50 per month. I get a 23% discount through the company that I work for. That discount doesn't apply to the 3GB plan but it does apply to the 5GB plan (strange). I wish I would have known that before. I was told that it didn't apply to the iPad's plan I had but nobody told me that it would apply to the next one up. So I bumped up my plan and all should be good.
Well... I can confirm that it can't be done through AT&T. I went to my local AT&T store today and thought everything was going to be good. The person that I talked to said that there was a way to do it. He swapped the numbers between the devices, activated the phone but couldn't activate the iPad. He tried it a few ways with no success. After that failed he suggested that I call AT&T because they can do more than a store can so I did that. Again, it got close and I thought it was going to work but no luck. The rep told me that it could be done if I was swapping the plan to another phone but it can't be swapped to an iPad. So... everything pretty much went back to normal.
But, I was able increase my data plan from 3GB to 5GB for an extra $8.50 per month. I get a 23% discount through the company that I work for. That discount doesn't apply to the 3GB plan but it does apply to the 5GB plan (strange). I wish I would have known that before. I was told that it didn't apply to the iPad's plan I had but nobody told me that it would apply to the next one up. So I bumped up my plan and all should be good.