Mysterious Phone Call

I had a bit of an odd experience last night. I was sitting on my couch playing video games. My cell phone, which was in my pocket same as always, rang. Granted, it was an unusual ring, not the tone I have programmed for incoming calls. The display screen announced that the call was from my grandma. When I answered, she seemed a little bewildered. Never in my memory has she called without a specific purpose in mind, so I thought it was odd that she seemed to have nothing in particular to say. After a bit of confusion, we discovered that she thought I had called her and she was waiting for me to get to my point! We talked for a little bit, and afterwards I checked my phone message history. The call was logged as outbound rather than inbound, so it definitely originated with my phone, even though I hadn't touched it.

Has anyone else ever had a cell phone spontaneously make a call on its own?

I hadn't been talking out loud, and the volume was low on the TV, so it shouldn't have been any kind of voice activation thing. Barring supernatural explanations, the best I can come up with is interference from some other device in my home, such as my wireless PlayStation controller or the cordless phone which was off but laying nearby on the table. I suppose if one of my neighbors had something putting off a strong signal, that could have done it, too.

Anyway, it was so strange!