Rapport is pretty simple, but it takes practice. I'm not at the level that I can consistantly influence someone across a room or get into deep rapport in short interactions, but generally if I can sit down and speak to someone I can establish rapport easily.
They key to rapport is pacing, and then the key to influencing is leading. If you only pace and don't lead, you'll more likely to be influenced by the other person than they will be influenced by you.
Many things can be paced. You can pace posture, gestures, facial expression, breathing, words, tonality, the rate of their speech, etc. You don't have to match them exactly and it is also possible to crossover pace. For example, you can pace someone's breathing by tapping your finger on a table.
For telemarketing, you'll only have auditory and verbal pacing, though you could also guess their posture and try to match that. Try speaking at the same rate, volume, and tone the person speaks, and listen for the vocabulary they use. You can also listen to see if they use more visual, auditory, or kinesetic words, and use the exact words they use. Accents can also be matched if you do it right. I was able to match accents of people, accents that I did not speak in until I spoke with them, and no one noticed.
The best book I've seen on rapport is "The Magic of Rapport" by Jerry Richardson.
One thing NOT to do is read your script as if it were a hypnosis script. I did that when I was in telemarketing (a very short time) and I put my co-workers and manager in trance all the time if they were near me when I was on the phone. The manager said I had a hypnotic voice and thought that I put everyone I tried selling to to sleep.