Okay, in preparation for the trip to Greece I started looking at cell phone options. The idiots at Cingular won't let me use international roaming until I've had my phone for a year (what bozo thought up that policy??), so that won't work--and would be prohibitive expensive, anyhow.
Via Matt Barrett's incomparable Athens travel guide I found information about Greece Travel-Phones, which rents cell phones and will deliver them to your hotel--but I wasn't sure I'd be able to get one with a cameraphone and MMS messaging, which I'd really like (mostly so I can post camphone photos from Flickr while we tour).
A little more online poking around led me to think that the best option is to purchase a pre-paid SIM card in Greece and use it in my Motorola v400 quad-band GSM phone. I checked with Best Buy (where I purchased it), and they told me it's unlocked--which is backed up by most of what I've seen on the online phone forums. I couldn't find anyone with a SIM I could test it with, so I'll have to take their word for it.
I sent email to the address provided for Greece Travel-Phones and got an immediate reply from the owner, who was extremely helpful. They do sell prepaid SIMS, and can deliver it directly to our hotel. He provided me with rates and options, and I was able to pay with PayPal. Yay! We'll be able to receive calls on the phone for free (011-30-693-970-0752, if you want to chat while we're there!), and outgoing calls, SMS, and MMS are reasonably priced. I bought it with €20 worth of credit, which I suspect will be plenty for what we need.
So...for those of you who travel internationally more than I do--is this likely to be a fairly simple process? Do I really just put the new SIM in and instantly have a Greek phone number? Are there any pitfalls I should know about? Any suggestions would be welcome, particularly if they're sent before I leave at lunchtime tomorrow!