A few items of clarification. This thread refers to two services by the same name - hotspot.
Anchor Free HotSpot Shield is a FREE solution. It is a SSL-based VPN (more on this) that installs on your computer in the background and is controlled by a system tray icon. The status is displayed in a browser screen. If you not careful, AF will install background processes and toolbars that are basically spyware.
HotSpotVPN is a paid solution. They have different flavors available. The originally supported PPTP connections (HotSpotVPN1) and SSL connections, now I think they are pure SSL (HotSpotVPN2). The three choices within SSL-based are 128bit (blowfish), 192bit (AES) and 256bit (AES). These refer to the encryption level - higher the number the longer the code would take to break. HotspotVPN2 use a freely available SSL-based VPN software called OpenVPN. You are free to install and your own server (outside of Belize) and client software and do this all on your own without paying

There are also many other paid SSL-VPN providers out there...
Why SSL-based?
SSL is commonly found in any secure internet transaction.
More on SSL The reason hotspotvpn2 works so much better is that SSL VPNs can work using UDP rather than TCP. UDP is a transport layer protocol designed for streaming audio/video. TCP is designed for data integrity - ensuring every chunk of data gets there. UDP doesn't care if one bit of a voice conversation is lost - it just keeps sending.
More on UDPBTL uses a technology from Bitek International to intercept and jam VoIP protocols. Read all about it here:
BTL VoIP Blocking Pride It is virtually guaranteed that anything inside a VPN tunnel as it passes through BTL's network is "private". Peter suggests that they may be using flow signatures to detect a bidirectional voice conversation "inside" a VPN. I find this very unlikely. They are probably keeping track of VPN traffic, seeing what hosts it is going to (in the US e.g.) and from what sources inside of their network. On a few occasions they have been known to slow down or jam traffic to a particular VPN service. Bottom line is they are very aware of how people are getting around their blocks - don't doubt that for a second.
Paid or unpaid doesn't matter. If you are using a SSL-based VPN that is running with a UDP protocol, paid (hotspotvpn2) or unpaid or whichever encryption level, it will bypass BTL's default blocks. If, for whatever reason, your traffic becomes of interest to them - it can be further degraded and potentially render your VoIP conversations dead.
Using a PC to run a networking service is generally not a good idea. I could go on forever about the inadequacies of Windows... When you have a PC-based VPN running, ALL of the internet traffic is going through it... not just the VoIP. This degrades your whole internet experience.
Enough technical jargon...
Finally, voice and video transmission on a BTL high speed line violates their terms of service. Not only can they shut you off but, in theory, they could go after you for damages. Some suggest that we should cower down to BTL and shouldn't talk publicly about their illegal blocking (and ways around it). I'm a fan of raising up and promoting enforcement of the law and viable alternatives to BTL.