Do I really nescessarily need a Google Mail Account for using my T-Mobile G2 touch?
Talking about Google Mail Account implecitely concerns more than the mail product alone: having a Google account like "xyz @ googlemail.com" provides the access to several (free) Google products like Mail, Calendar, Documents. All these products are web applications (rich internet applications) executed in and by a browser at the user machine (server) and storing the user data in the Google cloud (server).
Hence asking wether you can use your T-Mobile G2 touch without a Google account is asking wether you can use the smartphone without these net based 'background' applications and without storing your data into the Google cloud. Here is the answer:
Yes, you can use your T-Mobile G2 touch completely without the existence of a Google account. But in this case you have to maintain your conctact and calendar data manually. There still doesn't exist any method (or at least: I don't know any method) to automatically synchronize the PIM data of a Linux desktop system and the Android PIM data without using the detour to the Google cloud. Hence as private linux user you probably don't want to use your Android smartphone without a Google account even if you know that Google 'knows' your data (is the birthday of your wife a secret which must be protected against Google?): it's simply too boring to exchange PIM data as vcf file or anything else. And as commercial linux user you nervertheless don't activate your Google account, even if you therefore have to do the work of data synchronizing by your own typing hands: you probably have to protect your customer and partnership data.
The situation seems not to be a faintness of Google or Android, but a little gap of T-Mobile: we only need a little SyncML-application on our smartphone to link it for example to our PIM applicatgion evolution via the Linux the application MultiSync.