Thanks for mentioning VPN Unlimited. I gave them a try and decided to get in on the $19 for 3 years deal
Entirely possible FP is messing with your VPN traffic (or just isn't very reliable, it runs on Sprint after all). VPN Unlimited worked fine for me on both home DSL and T-Mobile HSPA+. VoIP calls (only about 15 seconds each to test) sound fine while on VPN Unlimited.
Just tested using mobile version of Google Voice web page to make a call. Even though phone was in airplane mode (but WiFi on) GV web page popped me over to my phone dialer to complete the call. So I will keep using the desktop version of web page to initiate VoIP calls.