Comcast is reasonably quick about transfers after you spend 20 minutes navigating through their phone tree. They only let you have one active transfer at a time. So make sure you list all the 800 numbers you need transferred initially. If you decide to go back for more as we did, you'll find out you must wait until your first transfer is complete before they let you initiate a second transfer.
Service is otherwise reliable and have not had any major complaints.
Difficult at first
Took a few calls and took a while but I guess it's done and should be fine from here. Thanks for your help!