The fax line will cost the same as the SIP? since it is essentially a SIP line with a couple of extra features. When you convert one of your SIP lines into a fax line, you will get an email with any incoming faxes. These incoming faxes will be converted into a .pdf file, and sent to you. You would want to whitelist fax@pcs1.ws as this is the email address that sends the faxes you would recieve.
Sending faxes will require the use of an email account. You would send the fax to the appropriate ITU-telephone-number@fax.pcs1.ws. For example to send a fax to 855-329-2377, you would send the email to 18553292377@fax.pcs1.ws. Sending a fax is however 10ยข+ per page. International rates will be extra, so this is only ideal for domestic faxing with occasional international faxes. The subject of the email is the subject of the fax. Any message in the body of the email will be on the cover sheet. The fax will also send you an email with the status of the fax sent.
When someone calls your fax line, and you turned voicemail on, then the fax server will pick up, and listen for 2 seconds for a fax tone. If it hears one, it will collect the fax, convert it to a .pdf file, and email it to you. If it doesn’t hear a fax, it will assume that the caller is a voice call, and send the caller to voicemail.
Since the fax line and SIP line are both the same price, you would want to weigh your decision. If you have a fax machine, you can use that to send and receive faxes. Domestic faxes will cost you nothing, but you would lose the voicemail feature. Any calls to your SIP account that has the fax machine attached to it will be doing faxes and nothing else.