How long will it take to start using service with a new number? November 04, 2019 02:43 Updated It doesn't take long at all. Once the SIM is inserted, activation should complete within minutes. Related articles How do I activate my SIM? I have more questions, how can I get help? I already have a SIM from my old service. What should I do with the new SIM I just received? How do I cancel my service? How do I return a new phone?