If you transfer your phone number that is associated with your DSL service, your DSL Internet connection may not work after the number transfer completes. Prior to porting a number, you should call your DSL company and for "dry-loop" DSL service, which will essentially disassociate your phone numbers from your DSL service.
I have used Ooma for more than half year now. Major benefit is save you cost of landline while still keep a landline like phone. Setbacks are 1. domestic calls are sometimes dropped. 2. Voice quality is not good for international call, I use it to call China. I have a 750K DSL. It might be the cause. I don't know. It saves me about $30/month. You might not think it is a lot money. But I can buy 27 McChickens, that is about 13 lunches every month. Haha.
I currently am using a cable modem with the ooma. I connect the phone line to the wall jack and it runs all the wired phones in the house, and it has worked flawlessly. I'm thinking of switching to dsl for various reason not associated with the ooma, but I have one concern will the ooma be able to transmit the voice service over my housed internal wiring?