Note, however, that not all Class 2 or 2.0 modems are created equal. Since a Class 2/2.0 modem is responsible for most of the fax protocol, deficiencies in the modem's firmware can lead to compatibility problems when connecting to some fax machines.
Faximum has done extensive testing of fax modems and has found that fax modems made by the following companies are above average in quality: Multitech, Telebit, and ZyXEL. This is not to suggest that Class 2/2.0 fax modems made by other companies will not work, but that you may find the performance in some cases is lower than with the recommended modems.