This is not a stupid question. The "world phone" capability of this phone is pretty damn good. Lots of radios. You can put a SIM card in the phone and it will work on any GSM network that Sprint will allow it to work on (and uses the same frequencies as the phone's radios).
Sprint locks the phone to prevent its use on domestic (USA) GSM networks. They talked about removing that restriction a while back, but it never happened. I would not buy a Photon to run it on ATT, TMobile, etc.
I have used various Sprint world phones in other countries. The results have been mixed.
The most frequent way I do it is to buy a sim at an airport or train station news stand. You get phone service for a low price, but I have never been able to get data to work. It has been a combination of user error and carrier policy, depending on location.
For instance, I was in Greece and got phone working, paid for data, and did not get the data. They (VodafoneGR) requires a contract to get data. Other carriers have different policies.
In Germany I got the phone working but bought the wrong SIM type for data. I understand that it should have been obvious to me, but I had a few too many Warsteiners on the train.
World phones rock. Hoping this one gets some good world testing...