I played with getting my fax modem to work with VOIPo. I did the usual stuff such as slowing the baud rate and attaching a DSL filter backwards. I never could get my faxes to be at all reliable. If you need to do heavy duty faxing with an office fax machine I suggest you keep a POTS line for it. For low volume faxing use the VOIPo Betafax feature for outgoing fax and get a $36 a year VOIPo Cloud Number for incoming fax to email. Or if you are really cheap (like me) you can get a free number from Voxox.com/ that will do free fax to email.