GPRS: up to 53,6 Kbits
UMTS: up to 384 Kbits
(= 6 times ISDN (64 Kbits/s))
from the Mobile Unlimited Brochure (see below)

See also:
Comparing Mobile Technologies

The following link doesn't work when I enter it directly :
Mobile Unlimited Broschure (in german) .
So I downloaded the file for the curious. Let me know, when the direct link doesn't give a 404 error message anymore respectively when the path is corrected (space, umlaut).

See also:
Comparison UTMS - GPRS (in german)