If they are seriously going to sue you then you will be served papers within approx. 30 days or so. However, if they were going to sue you, they wouldn't be harrassing you at the same time. *This is my opinion* but I highly doubt they are in the process of litigation.
One thing to note: Collectors are nothing more than telemarketers who are paid a commission to scare debtors into paying. The same person who is trying to collect your money can very well be selling chimney cleaning service part time on the weekends. There are virtually no prerequisites to be a collector (maybe a HS diploma or GED). There is no license or continuing education required to be a collector. Because of this, many collectors step over the line and break the law because most debtors think they have little rights. This is so far from the truth.
Many people don't realize this but the best bet when dealing with collection agencies is to be PROactive, not REactive every time they call. I would certainly recommend sending this agency what's called a "cease and desist" letter. IAAL (member of this group) had outlined a standard cease and desist letter in a previous post. Maybe you can reach out to him and get a copy. However, you can write this letter on your own. Simply type up a letter with ALL pertainant info (account#, their info, etc) and send it CERTIFIED MAIL to the agency. The letter should say in no uncertain terms that you want this agency to cease and desist all contact via phone about your debt. They must comply. As a result, the law states that all further contact must be by mail only. If they contact you by phone after reciept of that letter, GET A NAME! Do not answer even 1 question that they may ask you. Just get a name (even if it's a phone alias). Then hang up and contact a lawyer immediately. You now have a case.
Remeber one thing: You must make payments on your debt, even if it's $25 a month, otherwise you won't have a leg to stand on. If you do send any kind of payment consistently, you should be safe.
Hope this helps
Jeter