EssentialFax can now import faxes and phonebook from RKS Fax.
See the EssentialFax main menu under File > Import Faxes and
Phonebook (as of version 1.75 released
Jan 29, 2010).
Most of your faxes and phonebook can be imported intact - as long as they are still intact and on the same computer on which EssentialFax is installed.
A more detailed description can be found here.