The Apple iPad shifted 300,000 units on its first day, according to official word from Cupertino. That’s an astonishing number of touchable tablets. But while the world’s tech critics coo over Steve Jobs’s latest bestseller, some major questions still surround the mobile broadband-enabled, 3G edition of the iPad.

The first question on everyone’s lips is when it’ll land in the UK. The word on the street is that the end of April is when we’ll first see an HSDPA-friendly iPad, but that appears to be US only. Which leads us onto perhaps the biggest queries of all hanging over the 3G iPad for us Apple-hungry Brits: which network will be selling it here in Blighty? And more importantly how much will it cost when it finally lands, undoubtedly some time later than the end of April, on these shores at least?

First up, whoever sells the iPad 3G will need to have a big old stack of all new micro SIMs ready to roll, seeing as Apple has sidestepped the issue of punters signing up for bargain SIM only deals by loading the tablet up with support for the new micro SIM tech only.

At the moment, two networks stand out. O2 and Orange have both already slapped down orders for micro SIMs, putting them in prime position to land the 3G iPad. Web rumours have been flying that they’ll be good-to-go come launch, and only the most uninformed mobile type would bet against both signing deals with Apple. After all, they already flog the iPhone and stacking the iPad next to the mighty mobile in their stores would look rather tasty indeed.

So what about Vodafone? Rather enigmatically, earlier this year it came out and refused to say whether it will sell micro SIMs. And 3 has also suggested it won’t be in any position to flog the iPad when the 3G models finally lands in the UK.

But pricing is the real issue here. Apple and AT&T are selling open-ended contracts that will cost $29 a month for unlimited data. At the moment that translates to just £19, which seems remarkably low. Apple is unlikely to let UK networks sell data so cheaply on this side of the pond if it’s getting a cut of proceedings, so you can be certain that we’ll be paying something in the region of £25 for unlimited data. And don’t forget that tethering will doubtless cost a pretty penny on top of that if you want to use your iPad’s web connection on your Mac and PC.

The networks will need to battle Apple hard in order to get a fair deal for consumers. And the issues don’t end there. The iPad hasn’t even been priced up yet for us British gadget fanatics, but once it has we’ll have a better idea of what we can expect for monthly payments.

But with Apple’s previous in this area something Cupertino-haters love to bring up (see the epic iPhone 3GS pricing, MacBook price rises in the UK while US prices dropped), you can guarantee that being a 3G iPad early adopter in Blighty will be a costly business.