Speed Limit Alert for Garmin 350C

You can't.

The speed limit alert is part of the operating system for specific models so it's considered a "feature." The only way you could get this feature would be for Garmin to issue a new software release that would have no benefit for the company as it would impede your upgrade to a unit with this feature.

That is what I thought too. Thanks Box Car!

I kind of like it on my 3597 but it's only as accurate as the data on the map. Speed limits and areas change so it provides a general indication, but I don't trust it to be 100% accurate. I know state DOTs set speed limits according to a particular segment of a highway. The speed limit signs are not at the point a segment begins or ends, but are usually found within a quarter mile of where the segment starts. It also depends on the amount of change and the general area. Speed limits on arterials and surface streets are usually much closer to the beginning of a road/highway segment than they would be on an Interstate.