I' m currently have dsl & phone services with att. If i switch to Sonic today , how long will it take to start new service with Sonic. Do i need to call att to cancel their service. What is the down time during transition?
My personal experience is roughly 5-7 business days for legacy DSL, and around 7-14 business days for Fusion. Downtime should be no more than 1 hour. You should not cancel with AT&T--Sonic does it for you but it is a good idea to follow up with AT&T after the transition to insure your AT&T service has been terminated.
For the most part you will receive updates through email and you will get an ETA on when the transition will occur after several days from ordering.
DSLreports's Sonic forum has a lot of user experiences. Go there to get further details.