Motorola A780

I'm a Verizon customer, but I'm thinking of moving on to Cingular with this phone. I'm a bit confused though with the Motosync that comes with this phone, if I use Motosync, do I still need to get the data service or medianet service? I understand that Motosync uses OTA, but is there a cost attached to that by cingular on how much kb is downloaded, or is this a seperate case because it's a Motosync cablable device?

Thanks!