Now what happens. You end up on your favorite airport and you log on to the WiFi. Well to authorize yourself to the WiFi you have to key in your mobile number and you receive an SMS as verification code. But wait, where does it end up on your iPad's sim card? According to delivery reports, the SMS gets send, billed and accepted on the iPad but there's no way to see it. Bummer.
Ok then you take out the SIM card, put it temporarly into your iPhone and authorize that way? Ehm, the iPad has microsim's. If you put it into your larger iPhone slot, you risk of loosing it somewhere inside the case and never get it out. Fail.
Ok then you authorize using your iPhone's built-in sim card. Works, but then your iPhone sim card get's charged instead of the one from the iPad which you just added the "big huge data subscription".
In my case, I had to use my iPhone' sim card already for 400MB abroad last month and that's the biggest subscription you can get. So I wanted to have this solved and called Orange Switzerland. And guess what, their techies where able to solve the issue by allocating a fixed password. Bravo for their flexibility!