Yes. You may adjust the number of nodials encountered before disabling the modems in the /u2/vsifax/lib/vsisrv.ini file, under the VFXSCHED section, by setting the max-no-dials value to something other than the default value of 3.
Reference: http://doc.esker.com/vsi/6.1/en/referenceaddendum/index.asp?page=cfgfiles%2Ehtml
If you have further questions, please contact Esker directly.