Being a curious techie, I wanted to see if swapping a sim card from the iPhone 4 (AT&T) to an iPad 2 3G (AT&T) actually allowed one to use the iPhone 4 data plan on an iPad. Theoretically, if this worked, it could allow someone to avoid paying both the tethering and 3G data plans. My curiosity stemmed from these two threads: http://forums.macrumors.com/showthread.php?t=1108787 http://forums.macrumors.com/showthread.php?t=1110889 On online videos showing how to do this swap, they talked about changing the APN Settings on the iPad directly. Well, on the iPad 2 and apparently starting with iOS 4.x, there is no option to change the APN settings (under Settings | Cellular Data). I was pointed to a website that allowed one to create a custom APN setting that can then be downloaded to your iPad as a profile. So, I tried this website, downloaded the profile, did the sim swap, opened up Safari on the iPad 2, and there appears google.com. It worked. I just went to that one page as I really have no interest in doing this long term; so after I proved to myself that it worked, I put everything back to its original state. Funny thing happened about two hours after my test. I received both a text message and an email from AT&T hinting that I should consider getting a data plan for my 3G iPad and not swap working sim cards into it. And I received these only after visiting one website as a test. It looks like AT&T is cracking down, even on the lightest of usage. Anyway, I thought I would post this as a warning to folks considering doing this long term. I am not sure if I would have gotten more than a warning had I done some longer term data usage on the iPad. Below is the email I received from AT&T. ------ Dear JOEL MARCEY, We hope you are enjoying your Apple® iPadTM Wi-Fi + 3G! We value your business and want to ensure you're set up with the right data plan for iPad. If you have recently swapped a SIM card from your wireless handset into iPad, your data service may not work properly on either device. Please call us within the next 30 days at 1-800-331-0500 (or 611 from your wireless phone) and our team can help you establish service with an AT&T 3G Data Plan for iPad. AT&T offers two thirty-day data plan options for your iPad: 250 MB for $14.99 or 2 GB for $25.00. Both plans are available for advance purchase and auto-renew every 30 days to provide a seamless, on-the-go iPad experience on the nation's fastest 3G network. If you select the 250 MB or 2 GB plan, iPad will notify you at 20%, and 10% remaining, and when there's no more data available so you can decide if you want to add more data prior to the monthly automatic renewal or upgrade to the 2 GB plan. You can also change your data plan or cancel the automatic renewal at any time, without penalty. Our team is ready to help you activate data service with the right plan. We look forward to your call. You can also visit www.att.com/ipad to learn more. Thank you for being an AT&T customer. Sincerely, AT&T This e-mail was auto generated. Please do not respond.