Seems that if you have an iPhone 4, if you enable Personal Hotspot on your phone then you don’t need to invest in the 3G version of the iPad. Instead, you can save yourself quite a bit of dosh and instead use Personal Hotspot to give your Wi-Fi enabled iPad GPS features.
Zachery Bir, on his blog Urbanape, tells how he discovered this when launching Maps and hitting the Location arrow. Apparently, his experience has been verified by none other than WIRED who also claim that even if you have an Android phone that has 3G then you can do the same thing (though it probably requires you to jailbreak your device).
So, you will save $130 (UK prices TBC), which you spend instead on beefing up the memory on your fancy new iPad 2 ($100 will get you the 32GB model instead of the 16GB). Bear on mind that you may incur additional costs for £G services on your smartphone but this will probably be less than the extra you would pay for 3G services on your iPad from your mobile provider.