You cannot "divide up" a requested URL-paths into substrings using a "separator" character that can also appear in any of the substrings. Apache has no idea whether the category, brand name, or model number might contain a hyphen, so you cannot use a hyphen as the separator to parse out the variables in a deterministic manner.
A better solution would be to use slashes to separate your "fields" and then you can use hyphens within those fields:
Example URL:
site.com/mobile-phones/sony-ericson-phones/es-995.html
Example Rule:
RewriteRule ^([a-z0-9\-]+)/([a-z0-9\-]+)/([a-z0-9\-]+)\.html$ [NC,L]
Note the escaping on reserved characters, and that the use of [NC] allows [a-zA-Z] to be shortened to [a-z].
There is one downside to using slashes: The links to other pages and to included objects on each page must now be server-relative or absolute. In other words, you must use <img src
="/images/logo/my-logo.gif"> or <img src="http://site.com/images/logo/my-logo.gif"> instead of <img src
="images/logo/my-logo.gif"> on your pages.
An alternative is to use some other character allowed by the HTTP protocol as a separator, such as "." or "," or "~", but the slash looks most "natural" and will allow for keyword-in-URL indexing and highlighting in the search results. Be very sure that you understand these effects on search engine listing and click-through rates before using a non-slash character...
Jim
