My phone service with my Treo600 is with ATT, but I am able to roam onto Cingular. The ATT service at my house is "marginal" whereas I can see a Cingular tower from my back yard, so when I am at the back of the hosue, I find that I am logged onto Cingular, but when at the front of the house, the phone prefers to stay with ATT - and the service quality there sucks.

Clearly, the phone is set up to go onto ATT whenever possible.

Is there a utility available that allows me to manually select Cingular and ignore ATT when I want to?? If so, what is it called