All of you are not ALONE ! Most of us here in Singapore be it with Singtel, Starhub or M1 3G network, all of us with the "NewiPad" are sharing the same pain of this "Cellular data not connected" problem. When this problem occurred, one must power cycle or at least reset network setting to get the 3G data connection work again. A daily of power cycle 3~5 times for my new iPad was need. All methods like below tried but still DOES NOT fix the problem.
1. Reset Network setting.
2. Reset iPad back to default.
3. Changed Singtel APN name from "e-ideas" to "internet" still the same.
4. Changed a complete brand new sim card.
My current fixed was, called up Singtel ISP to reset my iPad 21Mbps 3G Line in their system. In my end, I need to power off my new iPad to complete the cycle. So far it has been working fine for 42 hours now.
By looking at the "General > About > Cellular Data Number" was "Unknown". This lead me to think it might be a bug in current new iPad iOS 5.1. To be more precise, it might narrow down to the "Big & Bad Qualcomm Radio chipset Driver" problem?
If that was true, jess.. I truly dislike "Qualcomm inside" devices. It make me come to remembered Dopod/HTC D810 the most funniest released WM device in history. When D810 first hit the market, it does not features any gps function at all when in true fact D810 did come with "Qualcomm" GPS chipset built-in since day 1. Dopod/HTC took more than 6 months to release a very crippled firmware that included Qualcomm GPS chipset driver with lots of trouble and start announce all the customers in the world, including those who's bought D810 more than 6 months ago. What a joke!
That's not all the "Qualcomm" funny facts. They then hit the wall again with Dopod/HTC Tytn-II, another WM cellphone with "Qualcomm 3D Graphic chip built-in, BUT WITH NO 3D DRIVER BUILT-IN". Hahaha.. what another big "QUALCOMM" historical joke of all time.
Anyway, hopefully Apple can found the actual trouble or fixed "might be Qualcomm driver problem again?" in the next iOS 5.2 release.
Until then, I've wishes everyone with the cellular data connection trouble eventually manage to solved your headache in any solutions provided by many and living happier with your new iPad, the same for me.