According to an interview with Philipp Humm, T-Mobile Boss Germany, in German Welt Online, T-Mobile is going to offer the iPhone 3G starting at 1 Euro in Germany.

T-Mobile is following O2, which already announced that the iPhone 3G is free depending on the chosen monthly plan.
T-Mobile offers the iPhone 3G for the symbolic 1 Euro when customers choose the highest monthly plan that runs for 89 Euro (~$136).
If you choose the lowest monthly plan (29 Euro (~$44)) then the iPhone 3G costs 169 Euro (~$259). T-Mobile keeps the same monthly plans that they offered for the original iPhone.
More details on Welt Online (German). Via Heise (German). More iPhone 3G News.