SER was developed by a team of developers employed by Fraunhofer Fokus, a German research institute. The iptel.org project was to build a website for Voice over IP information and a free Voice over IP service. SIP Express Router (SER) was developed as a part of this effort, lead by Jiri Kuthan. SER was offered as open source (GNU Public License, GPL) and the iptel.org website is still the entry point with SER information, as well as SIP tutorials and other related resources (though now not very actively maintained).

As another result of the iptel.org project, Fraunhofer Fokus spun off iptelorg.com as a commercial venture to further develop SER (for both open source and commercial purposes) and to offer services and software packages and support based on the iptel.org projects developed code (which by the way are more than just SER. See http://www.iptel.org/products/) Iptelorg.com got the main control and responsibility for developing SER, the open source SIP server. Jiri Kuthan and Jan Janak (Chief Software Architect) are both a part of this group. Andrei Pelinescu Onciul is another name that you can see on the serusers mailing list.

Some of the other former employees in the Fraunhofer iptel.org project launched another commercial SER-based venture called Voice System (http://www.voice-system.ro/). Daniel-Constantin Mierla and Bogdan-Andrei Iancu are two well-known names on the serusers mailing list.

This is how those known as the core developers were split in two groups. However, they all participated in the development of what we know as SER. In addition, other companies (like AG Projects responsible for mediaproxy) and individual developers joinded the group of developers. At the time of writing this, SER has 25 registered developers.