The Telephone company may or may not charge you a lot. I live in baltimore, MD, and we have verizon. I subscribe to the Wire maintenance Plan, so they charge me $4-5/mo (not even sure anymore) to guarantee the lines. if I have a problem, they will come out and look at the jacks, wiring, etc. to determine the problem. Once identified, they will fix the problem. HOWEVER, they have 2 levels of plans. The one I have it the reduced plan. The full plan is all-inclusive, in that even if I call them for service and they come out and determine that the phones don't work because my 900MHz cordless got dropped into the bathtub and I left it plugged in anyway so the line is getting shorted out, I am not charged. The plan I have only protects the wiring up to the wall jack and any verizon owned equipment.
Now...this is where it gets tricky, because other variables can play into this. My last apartment contracted a 3rd party vendor to come out and setup the phone jacks for every apartment in the entire complex to have a data port and a phone line. That way, they could attempt to sell broadband internet access and compete with the cable modem and DSL markets, and since the cable modem service was not allowed into the complex until a month or two AFTER the jacks were changedover, they got a jump on the competition. But...everytime we rec'd notice that the company was coming to swap our jacks over, they didn't show up. Finally, a main switch or something was thown, and we lost our phones. I knew my phones, answering machine, etc. were not to blame, so we called the phone company. they couldn't tell just by running tests, so they sent a tech out to troubleshoot. when the tech arrived, hhe checked my jacks and the main lines going to the NID. From the NID, the 3rd party vendor had installed their own equipment. So...the lines to the NID were fine, and my jacks were fine, and the problem was in the other vendor. I received an $80 bill and still had no phones. After about 8 months, i finally got reimbursed from the 3rd party vendor, but it was a pain in the butt.
Your best bet is to verify you have a solid dial tone and see if the phone seems clear when you talk (no static). If so, check to see if you have a wire maint. plan on your line. If so, call the repair line and ask for them to check your line. If not, order it, dial using your main line for another month, then call the problem in.
I did note that you said you had a friend wire an extension for the 2nd line. Is this a different line than the one you initially had installed? In other words, did you have another jack added? If so, i would either:
a) Buy a very long phone cord (25-foot or longer if necessary) or
b) temporarily move your CPU, Monitor, KYBD, Mouse, modem (if external) to the main jack for your 2nd line and see if the problem persists. this will help you isolate the problem to a bad jack or a bad line.