When you first signup for eFax, you're assigned a fax number. You're immediately able to receive a fax (without restriction), but the ability to send is hidden behind a monthly subscription. In order to do that, you'll need to sign up for a monthly plan of $17. That plan includes 150 inbound and 150 outbound pages per month, with an overage fee of $0.10 per page.
Unlike the other apps I tested, eFax not only emails you a copy of an incoming fax, but also sends a push notification — which is good, because the email attachment of your is an .EFX extension, something both iOS and OS X is unable to open. (Which is bad.)
Fax Burner is my favorite app out of the bunch, based strictly on the fact I was able to both send and receive a fax using a custom phone number for free within seconds of signing up. (On looks alone, JotNot Fax wins, but looks aren't everything.)
With this app you can send and receive messages using a fax number that expires after 24 hours. Once the number has expired, you're then reassigned a new number. You can hold onto a number for a year with an in-app purchase of $99.
The free account provides for a quick way to exchange important documents with a few limitations. A free account is limited to five total documents sent over the lifetime of the account, but you can receive 25 documents each month.
For someone who only sporadically has the need to send or receive a fax, Fax Burner's constantly changing number and limitations is a nonissue. For someone who requires the same number, or higher allotments for sharing documents the yearly plan is ideal.
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