It really depends on the carrier.
Sprint has only started unlocking the 5c and above since February.
Your problem
Virgin Mobile is an MVNO (Mobile Virtual Network Operator) using Sprint's network. Sprint will only international unlock an iPhone 5. Hence, Virgin Mobile which uses Sprint's network would only be able (through Sprint) to give you an international unlock.
Boost Mobile is an MVNO using Sprint's network. Since you'd be going from one Sprint MVNO to another that might be doable without a domestic unlock. However, Boost is not known to be a BYOD friendly carrier. You'd have to check with them. Honestly, you'd probably have better luck moving to Ting (another Sprint MVNO) which IS BYOD friendly to Sprint devices.
There is a loophole that is currently exploitable that is allowing the iPhone 5 to be domestically unlocked when Sprint submits an international unlock but it requires the device to be inactive on Sprint's network and any moneys being owed to have been paid.
In any case however, your phone is domestically locked to Sprint at the moment.