Yes that correct, Swisscom does nothing to provide a proper SIP. They have there partners, which are supported, but everything costless like asterisk is nothing for Swisscom, so Swisscom is nothing anymore for me. I habe a security System which makes calls over an analog line, I purchased an Cisco SPA112 connected it ti Sipcall and it works perfectly. The company EKB where I have the SecuriySystem I don’t let anymore in my house, because they told me, that I habe to order the bewest Security Device for 5500 CHF.
The Cico SPA112 costed me about 70 bugs, and my new provider SIPCALL is not expensive.$$By the Way, I run also asterisk on a rasperry, now I am Swisscomless, free and happy