MySIPSwitch: Use multiple SIP account with 1 phone - MySIPSwitch is a new, non-commercial, VoIP tool. The sipswitch ( http:// www.mysipswitch.com ) is a free of charge & open source web application which allows to use multiple SIP accounts on the same phone. To put it simply it means that you can use the call plans of different VoIP companies (using SIP) with one piece of hardware (IP phone, Softphone, combination of DECT phone + ATA)!
It does the 3rd party SIP registration so you can receive all your calls on the sipswitch account.