One more way to get rid of telemarketers or any unwelcome callers is to block them via Selective Call Blocking. You can block up to 12 numbers at a time.
You may need to have Caller ID for this. You'll need the phone number with area code of the number you wish to block.
Press or dial *60. The automated system will tell you whether you currently have Selective Call Blocking activated or not. Then it will ask for the first phone number you want to block, and if it wasn't activated before, putting a number in will activate it.
It also has an option to put in the last number that called you, but I haven't been able to make this work.
Anyway, I've now blocked one telemarketer and one fundraiser that never quits.