I'm switching iPhones and services, and I concerned about the process and loss of service (even temporarily). Any tips on how to handle it?

I bought an open iPhone SE to replace an older iPhone, and I'm signing up for a different service. They provide the SIM. And of course I want to port my old number to the new service. But I don't want to cancel my old service before the new one is set up. If I set up the new service before I cancel the old one will I have two functioning phones on the same number for a while? I'm not sure how to handle this and cause the least disruption to my service.

Once you port your phone number your old service will cancel your line, however you will still need to call them to ensure it get canceled properly. Only the new phone will work after the porting process has completed.

Porting the number over cancels the old line generally, so you will not have two working phone lines.

If you re not sure about the process of activating the new phone you d probably best go to a carrier store if you have one nearby and ask them to help with the process of switching the lines over.

This is generally how it goes:
You go to activate your new SIM through the carrier's page. During the account creation, it will ask if you want a new number, or transfer (port) your old number. Choose the port option. It will ask for that number and some other information like account PIN from the old carrier, port-out code/PIN and/or possibly your SSN associated with the old carrier's account.
The important thing here is to NOT cancel your service with the old carrier so that the number doesn't get 'lost'. Once the number is ported over to your new carrier, you can cancel the old carrier's service. In the mean time, the new carrier may assign a temporary number to your account so that you can use it while the porting process takes place.

If you don't know your account PIN or port-out code/PIN, you'll need to ask your carrier for this information and they should give it to you.

I think you would have to consult with the new carrier as far as number portability is concerned. There's no way you would have 2 phones with the same number.

1. Does the "older" iphone work fine? If so, there's no need to replace it. 2. Porting your number in will seemlessly transition services over to the new carrier, and no action will have to be done on your part. Just wait for the final bill in the mail, pay it, and it'll be done with. Also, remove the sim from the older device, since it'll be disabled.