EH304 I'm in the same boat as you; 22, just completed an economics MSc and want to use PhD to improve my skills and job prospects but not to enter academia.

If you have grades to get good funding and committed the PhD may be a good option and should at least to apply for Sept 2008. PhD's show an ability that cannot (arguably) be matched by any other qualification (MBA CFA ACCA.) What’s more, there’s a high chance your start at a level higher than undergrads. See

http://www.prospects.ac.uk/cms/ShowPage/Home_page/Advice_for_graduates/Chat/p!elmggX?mainstate=7&substate=7&cid=151

If your Maths is good you may be able to apply to quant posts too.

check this blog out for more info regarding areas that EconPhD may be useful in finance phdmbacfa.blogspot.com

If you decided to do it and your from the EU/UK try to get ESRC funding by making an outstanding proposal, a friend of mine gets more from this than he did from PWC

all the best,
billy