Can someone else use your t-mobile IP address?

Question

Like if you leave the coffee shop and forget to sign out, can someone else use that open IP address? I've been getting these huge bills lately and I don't think I've been using that much time.

Answer 1

Is it possible? Yes, I've done it numerous times.

Is it likely? Not really.

It requires not only grabbing the MAC address and IP, but also a MITM attack in most circumstances, in order to break the SSL encryption.