I believe "Anonymous" is correct on this. Plus if you were being served a summons, they do not call, they just show up. Also,a summons does NOT require a signature, just an answer, in writing, to the courts. They probably would rather you call them back and see if they can get anything(monetary) out of you, especially if the debt has passed the SOL in your state. Make sure to research when and if the SOL has been met in your state. If Anon is correct and this is a bottom-feeder, the odds are the SOL has passed. Doesn't mean they will not attempt to sue, but like anon said, it will be dismissed if you hv the proof it is an very old debt. When they continue the legal process, it is only in hopes that you won't show up in court and they win a judgement by default. 99.5 % of defendants don't show up, and end up paying even more. Also, there is a huge fine(for them) if they are calling you on a cell phone, so I would keep the messages.
Also, If I researched right they will need to file in my county for the law suite. Which is in Texas. And any debt I Might owe is way past the 7 years SOL here. I cut my cards up over 10 years ago and never used them since. The only debt I owe is on my house and its in good standings. :P
The good news is, the SOL in Texas is only 4 years. And to the second part of your question, Actually, they can file anywhere you may be living. I lived in TX, the SOL had expired two years before an agency attempted to collect on this debt, when I moved to another state, that states SOL was 7 years, so they filed...etc.. Fortunately the state I moved to has a "borrowing" statute, which means one state may "borrow" a shorter SOL for a cause of action arising in another state. My new state stuck with Texas SOL. This is my personal experience, and I AM NOT a lawyer, however I did have one represent me. Your situation may be different. If you are still in Texas, your good. And like I stated before...a process server DOES NOT CALL YOU AND GIVE YOU A HEADS-UP.
Thanks for the information able g. Got the 626 number call today stating they have been unable to contact me at my home... Thats funny due to I have been at home for the past 2 weeks under a work comp. injury. So full of it they kill me. They tried my brothers phone with the same messages. The only contact with him is his mail comes here. We dont even have the same last name. So ignoring them at this point.