The best resource for free support for Semantic MediaWiki is the Semantic MediaWiki user mailing list. The list is driven by an active user community, and answers to many questions can already be found in its archives on SourceForge among others, so a web search may also help.
Extensions to Semantic MediaWiki are often developed independently from the core SMW Project. Please check out an extension's website and installation files to find out whom to contact for support and where to report bugs. In general, issues related to extensions of Semantic MediaWiki can also be discussed on the user mailing list.
Some tips on sending a question to the mailing list:
If it relates to a specific extension, please include the abbreviation of that extension at the beginning of the subject line. For example, write [SMW] for Semantic MediaWiki, [SRF] for Semantic Result Formats, etc. (See here for one list of abbreviations.)
If it's a public wiki, please include the URL of the affected wiki page.
It it's not a public wiki, please list the version you're using of MediaWiki, Semantic MediaWiki and all other relevant extensions, as well as the version of PHP on your server (all of these can be seen on your wiki's Special:Version page).
Commercial support, custom development services, and trainings for Semantic MediaWiki are available from various sources. Service offerings can be announced on the Professional support page. Note that this is a publicly editable page, and that service providers listed there are neither explicitly selected, endorsed, or recommended by the SMW Project.
