This was the worst career choice I could have ever made. Even though as a salesperson I knew that the "no" answers and rudeness weren't aimed at me personally, it became very hard to take, no matter what the compensation was.
Telemarketing could be a good stepping stone into a more lucrative sales career-- if you have the thick skin necessary. Someone that can survive telemarketing deserves to work their way up through the ranks!
It was the absolute worst thing I ever had to do. You are constantly under pressure to make a certain number of sales a day or risk being fired. The trade off for this is that the jobs usually pay well and have great incentives if you have a high amount of sales. Be prepared to deal with all types of people with all sorts of dispositions. You will yelled at during one call and then chat about the weather during the next call.
The most important thing is that you have to be prepared to do whatever it takes to make the sale no matter what.