Cellphone Interference?

I have the Scion Security. (I know. I should have gone aftermarket, but it's easier for me to pay an extra $7.50 each car payment than a couple hundred at once.) Anyway, the other day I was waiting on my girlfriend and decided to call her cellphone to see if she was about ready to leave. Right when the phone started ringing, my alarm started going off on the other side of the parking lot I was in. I was holding my keys, but I was pretty sure I hadn't hit the panic button. I went over to the car to see if anybody had bumped into the car or something, but there was nobody around. As I was standing next to the car, I started to call her again, and right as soon as I started dialing, the lights on the car flashed on and off.

It turned out that her phone was in the car when I tried to call. Does anybody know if it's possible for a cellphone signal to set the alarm off, or trigger it in some way? I meant to test it to see if it happened again, but I haven't gotten around to it.