Yes the folks at Garmin are very good at phone support, in my limited experience. I called them in relation to a topic that Fattiresc probably already knows about, the GPSMap 498 does have an enormous database built into the unit of all of the most current coastal charts imagineable, but there is a limit to how far upstream you can navigate and still get information and to my knowledge, there is no chartage whatsoever of inland lakes.
I purchased the AC adapter w/PC connectivity hookup and it is a very worthwhile investment, I think, if you're going to buy something as complicated as this, unless you're extremely well versed in all of the functions already. I've spent hours exploring coastal areas all over the US, most places I've never been to but.........
I discovered a somewhat disturbing peculiarity to the way the charts adjoin one another at the headwaters of the Chesapeake Bay, particularly where the Elk and North East Rivers, having diverged, both tend northwards beyond the western end of the C&D canal. If you're not zoomed in to a range of .3NM or less, you simply run into "uncharted" territory.....major landmasses still show in outline, but that's it. It would seem that some sort of legend on-screen, similar to Google Map's notice that..... "high resolution photography is not available at this zoom level" might avert discomfit such as mine, thinking that I had somehow deleted something I was supposed to already own.
It was funny because it took the Garmin guy a few minutes of fooling around on his own GPS unit to duplicate what it was that I was seeing, and as soon as he did he too was surprised that all of the detail simply ended.
I think that the data cards that extend the coverage to rivers and lakes are about $200.