you are correct, you can use the $20 plan.

Cingular has 2 access points: wap.cingular and isp.cingular.. isp is for laptops, wap is for phones.. the only differnece is wap has NAT, ISP does not.

if you connect to isp.cingular and you are on a $20 plan, THEN you will be charged per kb.

otherwise as far as cingular is concerned, it is just your phone connecting, but connecting to WAP makes no differnece for us