Advice on new Phone for PAYG - Vodafone please ?

[Buckster]

I'm on a contract - but had stuck to my T39 for ages as was doing really well - call quality recently has got worse (ticking noise in background etc) - and want to replace it.

What would you recommend for around 70-130 please ?

I'm thinking a K750i which is £75

or a K800i for £130

Leaning towards the 750i at the moment - or am I missing a really good deal somewhere ?

I'm assuming a Vodafone PAYG phone will work with my Vodafone contract sim ?

thanks for any help, Mark.