I learned everything I needed to stop paying on credit cards here:
http://www.budhibbs.com/
(I had to make several attempts for the page to load.)
After 90 days (if I remember that number correctly) by law the credit card companies must charge it off as a bad debt and the letters and calls from them will stop.
Then and I don't think this part ever stops ... your debt on each card will periodically be bought by junk debt buyers and it will start all over again - the calls and the letters looking like they are from an attorney's office. Do not talk to them except to ask for their mailing address, the account numbers for the original debt and the collection agency account numbers, and current amount they they say is due. They will want to know why you want that. Tell them they will find out when they get the letter. If they are too difficult then hang up, call back and get the info from the person who answers the phone. Then simply send them a registered/return receipt "cease communication letter"
http://www.budhibbs.com/ceaseletter.htm and *most will quietly ride off into the sunset to go harass someone else. Then the next junk debt collector will buy your debt ... and the next ... but that might only happened 1-2 times a year for each card.
Here it is step by step with this little intro:
http://www.budhibbs.com/First.htm
"The collectors, bottom feeders, and junk debt buyers below likely purchased your account for pennies on the dollar. The law holds they must be able to provide legal validation if you are sued. When you don’t show up in court, or fail to respond to a summons you give them FREE money via a default judgment. My opinion, based on thousands of cases: the vast majority of these collectors NEVER have the legal documents meeting most court requirements. That fact will only help you if you challenge them and the papers they use to file court cases. If you are contacted by anyone on this list, get in touch with me for advice and referral to a local consumer law professional who may be able to assist you in beating these bogus claims and save you a LOT of money."
Statute of limitations varies by state. See the above link for a lookup on your state. Oregon is 6 years.