How do I send and receive faxes with a smartphone?

Receiving and sending faxes with a smartphones or tablet using Messagenet services are better performed via email.

To receive faxes you need first to activate FAXin or FreeFAX (free) - a regular landline fax number - on the Messagenet website.
Faxes sent to these numbers are delivered as pdf attachments to the mailboxe(s) you define. To let your smartphone receive these faxes, just add - if it is not already done - one of the email addresses of your smartphone (for example, the iCloud or Gmail email address) to the list of the email addresses enabled to receive faxes.

Email faxes will arrive from a sender that looks like, so make sure they do not end up in the junk mail.
If you are notified by your smartphone for new mail, you are notified also for new faxes.
The received fax - an attachment in PDF format - can be viewed directly on the smartphone, archived locally or in the cloud or sent to other people.

To send faxes, you need some Messagenet credit first - you can buy it on the Mesagenet website - then you have to enable the mailbox configured on your smartphone to send faxes.
If the number you want to send the fax to is (415) 996-1011 in the US, the TO recipient of the email becomes  or

If the number you want to send the fax to is (0)2079961011 in UK, the TO recipient of the email becomes  or

The international country code is required and has to be prefixed eiter by "+" or "00".

The text (body) of the message is the cover page of the fax, the attached pdf  will become the additional pages of the fax.
If you want to send to fax number ZZZZZZ a pdf document that already exists on your smartphone, just locate it, share it via email, possibly add some text and enter the TO address in the format like
It is possible to send the same document to multiple fax numbers at the same time specifying any number followed by - ​​for example,

Some smartphone app (such as Dropbox and Acrobat Reader) can be very useful to manage, retrieve and modify pdf documents to be sent by fax and to store pdf of faxes you have received on your mailbox.