Why does my friend's number show up wrong on caller ID?

For the last month, my friend's name and number have come up as unknown. For the last 2 days, it's showing as BT&S, LLC 305-938-5809. This is definitely not her, any business we are aware of, and not even close to the right number. I have Frontier for phone service, she has Comcast. I also had an incident last week - I called my sister's cell phone and left her a message. She received a message from my phone number, but it was a man leaving a message for someone else. Same time, said it was from my number, it was the only message she got. I haven't noticed any strange charges on my phone bill at all....I do receive unlimited long distance, so maybe I wouldn't notice? Does anyone have ANY idea what might be happening? I've never heard of anything like this. We're moving in a few weeks and won't have the same phone service or number anymore, so not too concerned, but just really curious about what might be happening. Thanks.