Many people contribute to the iptel.org website, resources, free SIP service, and open-source projects. A large number of developers employed by iptel.org/Tekelec contribute lots of code to SERi. The below list is a (small) start in presenting some of the names you will encounter in the iptel.org projects.
Paul HazlettPaul was the guy who initiated the ONsip.org (now merged with iptel.org) Getting Started effort by sharing his full configuration file on the serusers mailing list and asking for people to "break" it. He is the lead on developing and testing the Getting Started configuration files.
Jan JanakJan is a long time SER contributor and maintainer of many SER modules.
Vaclav KubartVaclav is the lead on the new presence functionality that arrived in SER 0.10.x. With subscriptions, notifications, and maintenance of contact lists etc, he has had the challenge of extending SER in a new direction when it comes to complexity in data models and dialogsi.
Jiri KuthanJiri is the "grand old man" of iptel.org. Active in standardization work and closely following (and guiding) the development work. His influence is far bigger than his presence on the mailing lists...
Simon MilesSimon is the editor of the SER - Getting Started document and is the sensible, no-nonsense guy focusing on "does it work?" and "is it needed?". Though being a former Linux kernel hacker, he does not do any iptel.org development beyond the document and website.
Nils OhlmeierNils is maybe most known as the author of sipsak, the Swiss army knife for SIP. However, he has a long-term relationship with SER (since 0.8.8 for those interested...) and he is currently lead on quality assurance for SER. That's why his commits seems to be of no pattern :-) Nils is also active in IETFi standardization work.
Andrei Pelinescu-OnciulAndrei is part of what can be called the "core team" of SER; those long-term, knowledgable guys who commit code to all parts of SER. You will often see Andrei commit code related to the various architectures that are supported by SER, as well as any low-level networking stuff.
Stefan SayerStefan is one of the SEMSi (media server) developers. His very enthusiastic about what SEMS can be used for (it is now a full B2BUAi) and is very welcome to ideas and suggestions.
Maxim SobolevMaxim maintains rtpproxy and the contact between rtpproxy and the nathelper module.
Greger Viken TeigreGreger was the administrator of the original ONsip.org website and Getting Started document, handling the technical infrastructure, test facilities and writing the SIP "theory" sections of the document. He is normally very visible on the serusers and serdev mailing lists and though commiting the occasional bug fix or feature to the CVSi, his primary responsibility is the website and community side of iptel.org
Miklos TirpakMiklos is one of the day-1 public SER contributors (initially: permissions module) who has been continuously improving SER's feature set and quality.