If you are using a different domain, the registrar may be different. Change from primary to secondary on old primary server. Assist customer in filling out domain modification template. At this point in time, the new provider is in complete control of the domain and you may begin to transition electronic mail services, WWW services, etc. at your convenience. Naturally, none of this can happen until the shorter TTL has propagated, so make sure you allocate enough time.
Old provider removes name from their server.
Remember that the party which provides DNS service does not have to provide all the other services. In fact, our experience has been that it is better to make the transitions slightly offset so as to eliminate DNS as a cause of confusion. Remember that the old provider may have already forgotten all about this transition. You should make sure to remind them about this step. Remove all references from both primary and secondary.