I believe that the reason I was offered $99 from Cingular is 1) Switch from TMo, 2) 2 yr contract with data, 3) minimum monthly voice plan at 59.99 (for 900 min roll-over). The voice plan is the closest one available at Cingular to TMo Get 1000 more national w/ unlimited nights/weekends. Of cause Cingular has roll-over advantage.
The monthly plan with TMo is $40 cheaper
than Cingular. This is the reason I hesitated to go with Cingular. Now TMo is offering me with one year contract at $349.00. This definitely seems a good deal to me. I can get a new device next year!
Coverage-wise, both carriers do a pretty good job for areas I live and visit most, domestic and international.
Another reason I want to stay with TMo service is the international roaming. TMo has excellent data roaming service in both Europe and Asia, places I travel most. I noticed that there is a new service (At least to me) called International Data Roaming Service at $19.99/mo. This means that no more extra charge based on KB. It is flat. This is a huge advantage for those who travel a lot internationally and depend on email and phone to get the job done. Cingular charges international data roam based on KB, although this option is available at TMo as well by default for international data roaming (?).