The data transmitted during a voice call and a fax transmission are converted to digital pulses in the same way, so sending is not the problem. The problem is at the receiving end. A receiving fax device has to be set to pick up the call before the voice call device, as it is the prompt of the fax transmission signal that makes the receiving fax switch from send or idle to receive mode.
So, if you are faxing over the internet the intended recipient's setup is a complicating factor.
Since faxing to landline fax machines via VOIP would incur a charge, you might consider a cheaper software solution such as eFax (www.efax.com
), which enables the receiver to receive the fax as a PDF document attached to an e-mail.
I hope this helps