I am pretty sure you can use the word you want in almost every context. Personally, I think of "arbeider" as a more formal word than "jobber". "Arbeider" sounds also more like a 'physical' kind of work to me. "Jobber" is the word I believe is most used in everyday life, while "arbeider" might be a little old fashioned.
If you mean you want a list of all four conjugations, yes, I do too. I look them all up on Wiktionary. There isn't an entry for telefonselger specifically, but there is one for selger, which I am realizing now doesn't quite match what Deliciae posted as the four conjugations for telefonselger. https://en.wiktionary.org/wiki/selger#Norwegian_Bokm%C3%A5l
Noun selger m (definite singular selgeren, indefinite plural selgere, definite plural selgerne)
seller (someone or something that sells), vendor, salesman