Just recently got my Ikea Family card through, and saw their deal for PAYG service.
I noticed today after logging in that on their "member benefits" page (where they list various topics) that on their Family Mobile promo they claim it is "Lowest price in the UK"
However, Asda PAYG has been around for 15 months and is cheaper... so the claim is a fib
Asda 8p/min 4p/text
Ikea 9p/min 6p/text
OK, after you pay an initial 10 quid to get your SIM, you can get an additional 3 quid from Ikea as an opening offer (for the first 10,000 applicants, and another 2 quid if you sign up for automatic top-ups) but if you were planning to use their PAYG for a teenager (who may send quite a few text messages a month) then it is 50% more costly than Asda.
Both seem to be using Vodafone for their network coverage, so there's only the price difference, nothing else to distinguish them (oh, but Asda does sell unlocked phones, and a good range of Vodafone models which will accept the Asda SIM, so maybe Ikea will add a couple of dozen mobiles to shelves in their stores in 2010!!)