"Do you believe that it is necessary to have a telephone?"
Translation:Tu crezi că e necesar să ai un telefon?
Yes, but only in a specific context. "Crezi" implies you're talking in second person singular (you) but "trebuie sa aveti" has to be in this context second person plural, so the person you're saying this to has to be part of a group of some sort that is is implied (e.g. family). Hope this helps