the softphone uses SIP i do not understand why it could not work on an ATA... i think it is more company policy to prevent customers from using this lower priced service with an ATA... if you have an unlocked PAP2 or other ATA device around I would plug in the SIP settings into this device and see if it will work... seems like they try to limit what you can do with this service from what I see on the website...

i think that it has more to do with the fact that the service is cheaper than the ATA device service, so they assume that people will not use as many minutes if they need to have there PC on, and use a headset to talk on the phone vs. having an ATA and being able to use any phone with the service...

i see that they do not allow you to change your number, or move the number to there standard ATA service... but I can not see any info on porting a number from this service...

they are not going to advertise on there site "hey, not satisfied with our service, take your vonage number with you when you leave"... so i would recommend to contact your new/potential provider and have them start the port process, since they are the ones who will have to do this....