Can you use your iPhone 4 sim with iPad 2?
Short answer: YES
After swapping the micro-sim card on iPad 2, you just need to change APN setting. iOS APN Changer
Real answer:
It will work for now, but AT&T might punish you for doing this.
Right after I got back home from purchasing iPad 2 3G(AT&T) version, the first thing I did was to pop out my micro-sim card from iPhone 4 and used it on the iPad. After changing APN setting, I was able to access 3G data on my iPad.
Why would I do this?
AT&T no longer offers $30 unlimited data plan on iPad. Currently, only way to get unlimited data on your iPad is to purchase the sim card from iPad 1 users who kept their $30 unlimited data plan active, or use your iPhone’s unlimited data plan minus voice(if you kept your old iPhone contract). The first option looks the easier but those sim cards go for $400+ on eBay. Since I still have the unlimited data plan on my iPhone, I decided to use it on my iPad 2.
So what is the problem?
Every GSM device has it’s unique device number. Since those numbers have patterns, AT&T can track which device a sim card is trying to access their data/voice network.
After putting back the sim card into iPhone, I got a text message and an email from AT&T notifying me of swapping the sim cards between iPhone and iPad. The email states, “your data service may not work properly on either device” so I should pick the right data plan for iPad.
When they say “may not work properly”, it means they will purposely disable it.
This is BS. The whole point of using GSM and SIM technology is to be able to swap SIM cards and make it just work. If you go to other countries, you can just buy SIM card and use it on any devices(unlocked) as you like. The funny thing is, I am using both devices that are sold by AT&T. There is nothing wrong in-terms of technology and the network. They just want to make more money.
My conclusion
My initial plan was to
+ use the iPhone 4 SIM on iPad 2
+ add a line to family plan with 200MB data and use it on Android/iPhone
+ Jailbreak iPad 2 and use it as a hotspot
If I use this setup, I would have to pay $25 more each month. The good thing about this setup is that iPad’s battery is much bigger than iPhone, so I won’t have dead iPhone in the middle of a day from using MyWi.
Due to the threatening letter from AT&T, I decided to get separate iPad Data plan for now. When I need to use data heavily on iPad, I will either tether from my iPhone or swap the SIM for that instance. I am going to see what happens to other people, and make final decision.