I am using a Sony-Ericsson P800 cellular phone on T-Mobile's U.S. GSM
wireless network.  The phone supports wireless data access via GPRS
for web browsing, email access, etc.  This is working well for me,
except for occasional outages.

My question concerns the Quality of Service (QoS) settings that are
available on this phone, as well as other GPRS-enabled phones.  They
are:

Precedence: Subscribed*, High, Normal, Low
Delay: Subscribed*, Class 1, Class 2, Class 3, Best Effort
Reliability: Subscribed, Class 1, Class 2, Class 3*, Class 4, Class 5
Peak Rate: Subscribed*, Class 1, Class 2, Class 3, Class 4, Class 5
Mean Rate: Subscribed*, Class 1 thru Class 18, Best Effort

(The asterisks indicate my current settings.)

What do these settings mean, and how does changing them affect my GPRS
data connection?