The main difference between iPad Wi-Fi and iPad Wi-Fi + 3Gis in terms of functionality: the Wi-Fi iPad is a device you can use to connect to the internet via wireless networks, but the Wi-Fi + 3G iPad can also be used on cellular networks, once you buy and install a micro-SIM from a carrier and purchase a data plan.
With a plan in place, your iPad can remain online away from wireless networks, and you can also buy a micro-SIM and data plan to connect abroad in countries with carriers that support the iPad. iPad Wi-Fi + 3G models also boast GPS capabilities, - the Wi-Fi only model does not - although both models have a digital compass.
UK iPad data plans
In the UK, four carriers have so far announced support for the iPad 3G: Orange, O2, Three and Vodafone. Three's data plans are the cheapest: £7.50 per month for 1 GB of data, and £15 per month for 10 GB. Vodafone comes in at £10 per month for 1 GB, £15 for 3 GB, or £25 for 5 GB, but doesn't include Wi-Fi via the likes of BT Openzone. Orange and O2 both bundle Wi-Fi with their plans.
O2's pricing is £2 per day for 500 MB, £10 per month for 1 GB, or £15 per month for 3 GB. Orange offers £2 per day for 200 MB, £7.50 per week for 1 GB, £15 per month for 3GB or £25 per month for 10 GB. More on rates can be found in our Best iPad data plans for UK buyers piece.
As always, read the small print to discover the terms of whichever service and plan you're considering, such as whether billing is one-off or a 'rolling contract' until cancelled, and how easy top-ups are if you run out of data. Note that 'spare' data doesn't generally roll-over with these kinds of plans, and so it's usually best to start with a lower capacity rather than waste your money.
If you're undecided about which iPad to buy and don't relish the prospect of splashing out an extra £100 for 3G capabilities you might never use, there is a third way: a MiFi mobile wireless hotspot. Three offers a range of prices for its wireless internet service, and the most relevant for an iPad owner is a one-month contract for £15 that gets you 5 GB of data.
Of course, you also need to factor in the £39.99 cost of a MiFi modem (and the fact you'll need to have it with you whenever you want to use it), although it will work with a range of devices (such as the iPod touch). Therefore, if you've multiple devices or find yourself with a Wi-Fi iPad and a hankering for very occasional 3G-based mobile connectivity, a MiFi is a good bet.