Faxburner is free and gives you virtual numbers good for 24 hours and lets you receive up to 25 pages per month for free. Also lets you send 5 total pages for free. Also because of the new safari uploading options in ios6 there is a trick to upload your fax to a website that does free faxes. If you send a receive a lot of faxes you might want to find a good app though, I think a good app would have the following features: gives you a dedicated number for sending and receiving faxes, stores the incoming faxes, push notification when you receive a fax, "open with..." function, and not too expensive, preferably a nice reasonable flat rate instead of charging you by the fax, or at least a low per-fax rate like 10 cents or something. Sme of them are 99 cents a fax. Also make sure they let you buy the faxes with in app purchases instead of logging into a website and using your credit card, for securities sake.
I'm looking for a free way to send and receive faxes on my pad too so I'm interested in people's replys to this thread. I'm thinking there has to be a website that offers free faxing services these days, there is no shortage of free VoIP services and some VoIP services work well with faxes.