The Linksys 4 line software upgrade has been discontinued.
All Linksys SPA941 and SPA942 IP telephones now support 4 lines (separate SIP registrations) without any license key simply by upgrading to the latest firmware.
For the SPA942, you should upgrade to at least version 5.1.10. Download Now
For the SPA941, you should upgrade to at least version 5.1.8. Download Now
If you purchased your SPA941 or SPA942 telephones from Telephonyware and need assistance upgrading them, please contact us.