I think an ipad works because many people believe they need a laptop. The reality is that many people just use their laptop to browse the web and read emails. This is a complete waste of processor power and as well as being much faster on an ipad it is also much greener. So buy an apple and save the amazon;)
I have the ipad 2 with sim card option - have a sim card in it but have not yet used it - all I have to do it just register and buy whatever minutes I need as and when I need it. Only used wi-fi so far as hotels we have been to had free wi-fi, but maybe I will end up buying some minutes while camping . . . then again a lot of sites also offer wi-fi. I like to have the option available though.
I've an iPhone 4, and I was looking for camping related apps too. I've managed to find some really useful ones, but they're not all free. I've yet to find one, but I wish there was an app that could find where you are and list all the outdoor and camping shops in the area...
360 Panorama - Great for taking photos of everything around you.
AA do a couple of handy ones - Days Out and C&C Guide. Along with the Pub and Restaurant guides, there's the B&B and Hotel apps that are handy to have loaded. HA Traffic - Highways agency traffic news (Takes you to the HA site, follow the link to open itunes and the app) Met Office or Weather Pro - forecasts and more. Go Sky Watch - Another app for stars and constellations. Around Me - as mentioned previously. Real Tide - if you're going to a coastal site National Trust - loads of places to see nearby English Heritage Days Out - English Heritage do one similar to the National Trust app.
Then there's the usual supermarket ones to find your nearest preferred large shops, Asda, Morrisons, Tesco's, Sainsbury's etc. Also Halford's do one, you never know eh.. Thomson Local and Yell - for the unforseen. iBooks - a little light reading.
Coleman do a recipe app Coleman Camp Recipes, but it's limited. Good for ideas if you're cooking with a campfire or cooker though.
There's a few to get you started, hopefully you'll find some of them useful. Enjoy...
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.