When buying an Apple iPad Wi-Fi+3G model, you have the option of choosing microSIM cards from Vodafone, O2 and Orange on the Apple [AAPL] site. The most expensive plan is from Orange and Vodafone where you get 10GB from Orange or 5GB from Vodafone. O2 does not have a £25/month plan.
Three in the UK has now announced iPad data plans and we see that they actually have the best deal for those wanting to use a lot of data through the month. Three are offering a £15/month plan that includes 10GB of data making it £10/month cheaper than the equivalent Orange plan.
The other tariff the company offer is for 1GB of data/month costing £7.50.
Three, just like other carriers, has made the plans contract free, meaning that you can purchase just 1 month of data and then cancel towards the end of the month if you choose to. The only things you need to really take in to consideration include checking for network coverage in your area, or the area you wish to use the iPad. Also, with Three you need to start and cancel by phone which can sometimes be awkward with the company from my experience in the past. With O2 and Vodafone you have the option of activating right on the iPad when needed. Hopefully Orange and Three will follow suit soon.
The microSIM cards from Three are available here.