Already using Prepaid service - upgrad to a Phone

Hello,

I am already using the $45 prepaid service since three months. Today I received a message that I could upgrade to an Iphone SE. I am really interrested in this. Since I want to use this phone also outside the US as soon as possible, I need a SIM unlock to be able to use it also with other SIM cards. On the AT&T page I read that the phone must be at least 6 months of paid service. Is it possible to credit my previous three months to this?

Thank you

Matt