Here's one that's kind of overkill to illustrate all the stuff you can put into a waypoint in GPX. Please pretend the dots are spaces. The forum editor truncates contiguous spaces to a single space and there's no way to override it that I can find. It's a pretty good bet that Streets&Trips will ignore the Garmin <extensions> section.
<wpt lat="50.5871390" lon="-127.3030240">
..<name>7 Hills Golf Course</name>
..<sym>Golf Course</sym>
..<extensions>
....<gpxx:WaypointExtension xmlns:gpxx="
http://www.garmin.com/xmlschemas/GpxExtensions/v3">
......<gpxx:DisplayMode>SymbolAndName</gpxx:DisplayMode>
......<gpxx:Categories>
........<gpxx:Category>Golf</gpxx:Category>
......</gpxx:Categories>
......<gpxx:Address>
........<gpxx:City>Port Hardy</gpxx:City>
........<gpxx:State>BC</gpxx:State>
......</gpxx:Address>
....</gpxx:WaypointExtension>
..</extensions>
</wpt>
Here's just the parts that would interest you to play with (just the basics, no <extensions> required). You can put anything you want in the <cmt> or <desc> fields, including addresses and phone numbers. As I mentioned, I have no idea how much of this Streets&Trips will import. I know that there are programs out there to convert from CSV files (from e.g. Excel) to GPX and will create the fields above as well as those below.
<wpt lat="50.5871390" lon="-127.3030240">
..<name>7 Hills Golf Course</name>
..<sym>Golf Course</sym>
..<cmt>This is a comment.
It can be multi-line with line breaks in it.</cmt>
..<desc>This is a description.
It can also contain line breaks.
You can put pretty much anything in comment and description fields.</desc>
</wpt>
For your specific purposes, in the Garmin world the <sym>Golf Ball</sym> argument will tell the Garmin navigation device to use whatever symbol has been assigned the name of "Golf Course" when displaying this waypoint. In Mobile PC and Mapsource and on most of my Garmin units it's usually a golf ball on a tee but in one unit I think it's a green circle with a flagstick on it.
Other symbol names in Garmin-ese would be "Circle with X", "Pin, Red", "Lodging", "Restaurant", "Residence", etc. On most units the "Pin, Red" will be a red pushpin of the sort with the little round ball on the end rather than the default pushpin shape in Streets&Trips.
I don't know if any of this will be useful but I hope that you at least find it interesting. :)
...ken...