I have had this happen a lot of times with VOIP phones, I think it is when you dial someone, and hang up, the call glitches out and calls yourself instead, all the phone knows is to make a call but not to who, so it does itself.
Calling you're own number is just setting up your voicemail mailbox. So my guess is if you're getting called by your own number, it would only access the voicemail mailbox setup.
It's very common... Telemarketers often block their numbers and use yours as their caller id. It's a really shady thing to do and weasels around FCC regs. Frankly, the practice should be illegal but they haven't updated the laws.