VoxUpgrade allows you to purchase additional SIP Registrations in lots of 5.

Have you already purchased VoxLite and have now decided you need more than one SIP registration. Now you can upgrade the number of SIP registrations by purchasing a VoxUpgrade. VoxUpgrade is only available to VoxPremium members. That is, you must already have signed up for one of the folloing: VoxLite, VoxPro or VoxExtreme.  

Each VoxUpgrade gives you 5 additional SIP registrations for US$15. If you want more than 5 SIP registrations simply specify the quantity you require. Two VoxUpgrades will get you 10 SIP Registrations, three VoxUpgrades will get you 15, and so on.

For example, if you already are a VoxLite subscriber and you purchase one VoxUpgrade you will end up with 6 SIP registrations.  Your member details page shows how many SIP Registrations you have with the label Registration Limit.