My Un-Activated Palm Pre Plus can still use mobile hotspot?

I just bought a new phone, and i was looking at my old Palm pre plus. It is completely un-activated. No account hooked up to it. I grabbed the phone to see if mobile hotspot worked and it did? I had my hotspot working in a non wifi hotel room. I didnt keep it on because i didnt want my account to be additionally charged. So i am wondering; Can my account be charged for it? And why does hotspot still work?