I recevied two letters today from two debts that I know that I owe. They are some old utility bills from when I recently moved. Looks like they were just assigned to collection agencies. They aren't showing up on my credit report and I would like to keep it as such. I know that some agencies won't report if they are paid in the first 30 days. \Is this generally true? Thanks.
I don't think there is any reliable answer to that question. Each collection agency has it's own policies on that. If you are worried about your credit score you might not want to pay them at all because if you pay they will probably report it as a paid collection and that rating is one of the worst hits your credit score can take. The older a negative tradeline becomes the less impact it has on your credit score. That is something you may want to take into consideration.
I've had this happen a couple of times, especially with overlooked medical bills. What I've done, is mail a payment to the OC, and then a couple of days later mailed a DV to the CA. So far, I've never had one of those collections appear, but YMMV.