Yes, you can keep your current fax number(s) and port it to FAX.PLUS. This way you benefit from all FAX.PLUS features without changing or losing your existing fax number. Once the porting is done, your number can be used as an inbound and outbound fax number.
Please note that before requesting porting, make sure that your current provider supports porting, your fax number is active, and there is no unpaid balance.
See also: How does the porting process work?