I like to check numbers I don't know too. It's nice when you can trace them. If it's a home number, as opposed to a business (telemarketers and other numbers of the same caliber), and it's listed, it shows up in a search, otherwise usually nothing. I like when others have posted the numbers to let people know who it is calling.
I find with magic jack, sometimes strange looking numbers call, but that's because their not being detected correctly, or sometimes it's from a private or blocked number.
Yes, it could be texting from a computer. And yes, if the phone number is still the same, then it could very well be messages for the previous owner.