I bought a Mobalphone that only works in Europe a few years back (usually advertised in airline magazines). You attach it to your credit card and only get charged as you use it. You'll get a British cell phone number and the rates are quite reasonable (with no plan). If you travel to Europe frequently I would strongly recommend it.
An alternative that is really cheap if you don't need a cell phone with you at all times is PennyTalk, where you can call for about anywhere very cheaply.
Last year I wound up on a project all over the UK and central Europe. I did lots of research for cell phones and ultimately found the cheapest route was to just buy a cheap/working unlocked quad band GSM phone from Ebay. I got a Motorolla flip phone for something like $50 with all the accessories. I went with this for two reasons, it was cheap and more importantly there was a ready supply of accessories available in the areas I was going.
Once in the UK I simply went to a mobile store and bought a prepaid SIM card. I found Orange to be the cheapest/best deal @ 5p a min to call the US with inbound calls free in the UK but you can shop around when you get there. Just make sure you ask for the card for the type of calls you will do (local/call the US, etc). I could "top off" the card at pretty much any convienance store. I had flawless service, limited my costs, no contracts and I could simply reuse the phone anytime/anywhere with a new SIM card.
All in all for two weeks I think the real question is do you think you'll use a cell phone that much? Will you or someone you know make a similar trip overseas again in the not too distant future? If yes to either, buying a phone might be your cheapest route
zukracer - Excellent tips. It's been awhile since travelling overseas. I already have a blackberry/US only/verizon. Based upon your comments, all I would have to do is go to a mobile store overseas get a SIM and a plan? Since I recharge using USB to a notebook, I'll need a power converter accessory, too. Did I miss anything?
TJC, I think you'll need a new phone if your BB is verizon, us only. Verizon is a CDMA technology, as is Sprint here in the US. Over in Europe they are almost exclusively GSM, which is what AT&T runs here in the US. If your BB is a world phone, you can get them to "unlock it" and then you can use which ever SIM card you would like while overseas. The key to buying any GSM phone is to get one that is "unlocked". Otherwise you will be tied to using that company's SIM card.
My new Sprint BB world phone is now "unlocked" and I can run on the GSM technology when CDMA is unavailable but still just use my Motorolla Razr to make sure I never pay the outrageous fees. I sync my phone contacts from my laptop so it all works out.
If you do have a GSM SIM capability on your phone, you'll likely just need an adaptor for the electric plug, my BB ac adaptor will swing 120/240 automatically, you'll want to just check yours to be sure. Also if you spend any time in a car while there, your US cig. adaptor will work, same 12v systems :)
It is also probably important to note that most of the companies there will sell you a "disposable" phone that works on that company's network. I liked having my own GSM phone because I make trips regularly and to many countries. I actually have a UK, France, Germany, Italy card that I simply slide in/out as I visit certain areas. I then update my local Vonage phone number to point to my current international phone number at the time for people to call me. I dont pay for inbound airtime on the cell but do get charged from Vonage, though the rate is fairly cheap. Also allows me to move freely around without having to update folks all the time ;)
Hope this helps :)
There are a number of cheap GSM phones on ebay right now, the search words I used were unlocked, gsm, quad band. My advice is look for something mainstream in case you need to find accessories while overseas. A coworker had a samsung phone and couldnt find an adaptor for 2wks while we were out in the countryside. There were motorolla accessories everywhere ;)