The travel section of my newspaper has a blurb that says TravelCell is offering a free cell phone rental for international travelers. (usually $24.95 a week).
The website www.travelcell.com does not indicate this offer anywhere, but it might be worth it to phone and ask, if you are considering renting a phone.
1-877-cell-phone

This info does not tell you the obscenely high rates this outfit charges for calls...several threads on this topic already exist.

Well, then - that must explain how they will profit from the offer..

We took them up on their offer last year just to have a cellphone in case of some dire emergency. We never used it. We don't normally carry a cell phone, but for $15 shipping (or whatever it was) it was OK to have in the glove compartment just in case.

You have to use the special code: NR512 when you are going through the signing up procedure.
My advice is this: If you need the phone for regular use, calls within Europe and keeping in touch with home, and you travel to Europe on regular basis, buy one, but if it's a once in few years trip to Europe and all you need is to make sure that your family could reach you in case of an emergency, it is a great deal. Actually incoming calls are free, so as long as they know your number they could call you daily. I do believe there is a minimum daily charge of around $4.00, but again, if all you will needed for is an emergency, or receiving calls from US, it is a great deal.