We purchased a Dell 2135cn for one of our departments and after setting up the unit was getting great feedback. Well after about a week I get a call stating they are not getting any incoming faxes. The previous fax machine worked fine. After talking with the people I realized it had never received any faxes. Hmmmm.
After speaking to Dell they had me check one or two things but after those checked out they sent us out a new one. They were very quick about this and the new unit even included new Toner. Got it set it up using the same seetings as the existing unit it's receiving faxes like a charm. I would love to know what on the other unit was the problem but will be fine with the new one just working. The Department that uses it loves it.
Overall it is a great MFP. My only complaint is that it does not have a Duplex Option.
Update - 7/21/2010 - If you have the "Junk fax" Option I would try disabling this. It may fix your problem.