@Damien2011 wrote:
I'm going to switch carriers soon and port my two numbers but I don't know exactly when to do this during the billing cycle. I'm not under a contract with either phone - both are paid in full. My bill is due on the 26th. My billing cycle ends on April 3rd. Is the bill that is due now for service that already occurred or will occur in next month? I've read that I should port about 5 days before the billing cycle ends but if I'm getting billed in advance, why would I pay the bill that is due now? So confused.
It appears you have never taken a close look at your bill because it indicates which time period the bill is for.
For example, I received my most recent bill around Feb 18. The billing period for this bill is listed on the first page, Jan 16 thru Feb 15 and it is due on March 7.

Looking deeper into the bill, each of my 4 lines lists the line's charge and the period for those charges, in this case Feb 16 thru Mar 15.

So to answer your question, you SHOULD pay your bill because that is money you owe Verizon and to do otherwise would cause Verizon to negatively impact your credit score AND Verizon would eventually blacklist your device(s) due to non-payment.
A good time to port your number(s) would be as you stated, a week or so before your billing cycle ends in order to ensure the port would be completed prior to your billing cycle ends and you getting charged for another month of service.
So, if your billing cycle ends on Apr 3, that means you have already been billed for service thru that date. Your current bill is for service thru that date. You have used the service and therefore owe the money and should pay the bill. Initiating a port on or around Mar 28 would give a good safety net to ensure the port would be completed and you getting charged for another month of service.