On this site we mostly air our problems and complaints so I thought I would balance it out with something that actually worked!
One of the features I liked about the Photon was the "world" radio capabiltiy (GSM) and the SIM card. I went to Spain a couple weeks ago (pictures at http://gallery.newts.org/main.php?g2_itemId=36908) and wanted to have data and also phone access while there. I searched around online some and ended up buying a prepaid SIM from http://www.holidayphone.com/. For about €50 I they mailed me a SIM card before I left and handled all the legal stuff (some countries like Spain won't sell anonymous chips or phones, they need your passport for foreigners). this includes about €5 of phone credit and 1G of data for 1 month. I also paid a little extra for another 1G add on. Their service also includes a temporary US phone number that will forward for free to your GSM number so people calling your US phone will still reach you over there. Oh and incoming calls are free.
Before you leave the US you enter a code to set up forwarding to your temporary number. Then when you get there you can put your SIM card in and enable GSM (I usually have it disabled). When I got to Spain, boom, I had a signal! Alas there was no data. It took me a day or two with tech support (they were responsive) and some mucking with APN settings to get my data to work.
Eventually I did and I could upload my Facebook photos right away. And do all the stuff I normally do.
In Barcelona I usually had a decent 3G data signal but it really varied quite a bit. The littly alleyways really block the signals. Some times I could do streaming G+ video chat and other times I only had a "G" signal (never saw that icon before!). Sometimes I got an "E" icon. I have no clue what that is but for me it meant virtually no data.
I installed a data usage app so I would know how much data I was using. For 2 weeks of heavy use I used about a gig of data and probably didn't need the extra gig.
Another gotcha was $15 on my Sprint bill for call forwarding that I didn't expect. Sprint charges $0.20 per minute to forward my calls. If I knew that I probably would not have forwarded incoming calls.
The Spain SIM did not work in Amsterdam and I never saw a CDMA signal.
When I got back the US the code they gave me to disable forwarding didn't work. I had to call Sprint support and they gave me the correct code.
All in all it was fun to have connectivity while traveling. I will have to try it in Asia on my next trip (or Sprint has umlimted 4G data in Taiwan for daily fee I might try).
I'm guessing the "G" icon you saw was for GSM or GPRS and the "E" icon was for EDGE. These are older technologies that Sprint (and Verizon Wirelss) never used, but the rest of the world (including T-Mobile and AT&T Mobility) did.
Next time, don't forward your calls unconditionally. That is what Sprint charges you the $0.20/minute for. *72 is for forwarding of all calls, immediately, when the call is received. *73 is for call forwarding of unanswered calls. So, when you dont' answer after four rings, instead of forwarding your call to voicemail, Sprint will forward the call to number you specified after dialing *73. Sprint does not charge for this feature. I've used it on several phones for third-party visual voicemail apps.
I also really enjoy having a world phone for travelling out of the US. Next time I go out of the country for several weeks, I will try the site you provided for the European SIM card.