The first time that I took a job as a telemarketer, I asked a sheilah and was told that it was muttar, and I’m almost 100% certain that it was not for a tzedaka organization. It was for a Frum organization, but it was a business, not a tzedaka.
The only time I had a yashrus issue with a telemarketing job was the one time I worked for a goyish place, and I felt like they were deliberately taking advantage of people, and possibly being dishonest as well, although it was hard to tell if there was any clear- cut dishonesty going on. That time, I asked a sheilah and was told to quit.