droid pro 3g/umts issues

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hi...

i bought an unlocked droid pro from ebay.com. now i use the phone with a t-mobile / telekom.de sim card - so far so good ^^ but i have a strange problem with call's if the phone uses the 3g network. if i make a call - i have no free line signal and the call starts with a delay of 6 seconds. if i force the gsm/edge network, everything works fine :/
i tried everything: factory reset, battery pull, sbf flash and.... but nothing helps

any other ideas?! is it a baseband problem or....?!

no one has any ideas?! need HELP...thats annoying :/