It's huge. The most recent OFCOM market report[1] reckons just over half of all mobile customers in the UK are on PAYGO. Don't under-estimate the UK pre-pay (PAYGO) market. It's quite easy to, because most people reading this are probably on contract themselves.
Not only is pre-pay half the market in the UK, it's by far the hardest to retain. Pre-pay customers aren't loyal (partly because they're not locked in to contracts, partly because they tend to be price conscious), and because they skew young they tend to be the customers more likely to both a) use SMS, and b) switch to things like WhatsApp.
I find that really surprising because phone service is now just so damn cheap in the UK. After a cashback offer, I'm effectively paying £5 a month for more minutes, texts and data than I can hope to consume. I guess my needs are relatively modest, but so (I imagine) are most non-business customers'.
Not only is pre-pay half the market in the UK, it's by far the hardest to retain. Pre-pay customers aren't loyal (partly because they're not locked in to contracts, partly because they tend to be price conscious), and because they skew young they tend to be the customers more likely to both a) use SMS, and b) switch to things like WhatsApp.
[1]: http://stakeholders.ofcom.org.uk/binaries/research/cmr/cmr12...