Well, I just put in a bunch of garbage for my TCP settings, to see if perhaps some validation of the settings occurs to determine if they are accepted or not.
Looks like there is some validation occuring.
My garbage settings reverted to my previous "working" settings after restarting the BB.
Since none of your settings have yet been accepted that may explain why after resetting you continue to revert to empty values.
a) the settings you are entering are incorrect and not being recognized by whatever authority they are being validated against
b) your settings are correct, but the authority that is validating them does not believe they are valid for your account (e.g.- perhaps your data services are not properly provisioned; isp.cingular vs. wap.cingular as Mark pointed out)
1) try both wap.cingular and isp.cingular
2) if that doesn't work, seek professional help (again):
a) explain to them what you are experiencing
b) verify Cingular has an APN setting on your account for both "isp.cingular" and "wap.cingular"
c) verify you have the appropriate data services provisioned on your account (i.e.- the "WIX" line items referred to above)