cingular network numbers

I'm seeing both 310410 and 31026 coming up in my market (MSP).

Is 31026 the old ATT GSM net and 310410 the newer Cingular net?

My phone (MPx220) will let me pick one of the two as 'preferred', does
it make a diff which one I grab of should I not pick a preferred
network?

thanks

.