Steve,
As Lee mentioned, you'll need to check the "Input Voltage" ratings on EACH of the devices you'll be travelling with. It's quite likely that all will be rated for use at 100-240 VAC, which means you'll only need inexpensive Plug Adapters.
One point to stress regarding your IPhone 3GS is that it's important to disable the data portion while in Europe, as the data roaming charges can be VERY steep! Of course, if you're arranged some type of international roaming plan with AT&T, that changes the situation. Be sure to check this every so often, as I've heard a few reports of the data section "mysteriously" turning back on.
I wouldn't bother looking at Voltage Converters just yet, as you may not even need one.
Happy travels!