Default [Q] VPN for public WiFi w/o using VPN for UMA

I got a T-Mobile phone with UMA capabilities so I could pick up on Wi-Fi hotspots to make phone calls if away from my home, but I want to avoid sending my sensitive data over pubic networks. Data is too easy to pick up on a puiblic network for me to feel comfortable with just letting it hang out. So, I'm trying to find a way to use a VPN for my everyday data use but still allow UMA to do its own thing. I tried to just use a VPN to encrypt all the traffic, but my phone traffic (Calls & texts) never send or connect to T-Mobile network in order to send messages or make calls. I don't know if its possible but I am determined to find some kind of work around. Anyone else had any luck with this?