Since there is already an unlocking method for the iPhone OS4 (
Sn0wbreeze), why don't you get your iPhone unlocked and use it in Germany?
Except for the first iPhone, which didn't support 3G at all, all following iPhones support the 3G band used in Germany (2100 MHz), so your iPhone would be perfect.
If you prefer getting a separate phone for Europe, I would recommend the T-Mobile Pulse (aka Huawei 8220), which will get an update to Android 2.1 (the almost latest version of Google's operating system) and which is
currently sold for just € 150 (in mint condition).
For the same price you could also get a used Nokia E71 from eBay (don't buy the US-version, which doesn't support the European 3G frequency!), which is great for eMailing due to it's QWERTY-keyboard. However web browsing is a pain on this handset.