With regards to buying a K800i from the catalogues as recommended in another guide.
A word of warning, I ordered one from Freemans on 21st June, originally quoting 3 weeks delivery, then early August delivery, now hopefully end of August but not confirmed. So that's 9 weeks lead time and still not guaranteed either.
So to hedge my bets I ordered one from Great Universal on the 16th July. I have never had an eta from them, but they too can't give me a guaranteed delivery date and are suggesting I may get it by the end of the month.
Same with Argos, they're out of stock as well. It would appear that all stock of K800i is going to the phone shops for contract sales and only when demand slows will they supply the sets on PAYG. I gave up waiting and bought one on contract from O2, which actually worked out cheaper than PAYG (that particular cheap contract has now closed), ordered it Monday, it arrived next day.
So if you want a K800i on PAYG and don't want to wait months, then ebay is the way to get one. The usuall caveats apply. Make they have good feedback, don't buy high value items from newbie sellers regardless of how cheap it is. Check if they have sold mobiles before and don't buy from sellers who hide their feedback.
By the way, it's a great phone, make sure you use your 3G sim, fantastic if you're in a 3G area, if you're not in a 3G area it will just default to normal service until it picks up a 3G signal again.