Looking at changing from vodafone to Snap naked vdsl.

If I want to keep my phone number what is the process? Do I change it to 2talk first and then change my broadband over or do I complete the online details with snap and wait until the naked dsl connection is completed?

I don't really want to have downtime if I can avoid it.

Second question, what is the Fritz phone like that Snap can provide? Is there better for the money ($138)