cant dial local numbers

[mulletpilot]

hey guys, im new to the forum...but i have a quick question.
i have an unlocked cingular treo 750 wm5 which was working beautifully. then overnight something happened, and now every time i dial a local number i get the 'this number is long distance, please wait while we connect you'...which eventually doesn't connect. the only way around it is to add the area code every time i dial.
when i flip my sim card into my alternate cell phone, this doesn't happen, i can dial local numbers without the area code, as per normal. im sure its just a setting somewhere in my treo, but i cant find it. i tried a hard reset...but no luck. anyone got any suggestions???