I have only done this with a CSV file, but it worked for me and is the format used in other CSV's I have downloaded.
Just add that information into the 4th column of the CSV file edited with POI Editor for Garmin or make new POI file with http://garmin.gps-data-team.com/poi_manager.php
The first two colums are for coordinates, the third for major title information and sub title information can be added to the fourth column. I don't know that the length of field maximum is, but I believe it will keep wrapping on the display for at least 8 lines.
On Nuvi 760 - no problem to have 3 nuvi pages of text - and that is not the end of limit ... try POI Manager. Save your file using the button named GPXx (GPX extra info).
With the GPXx button you can save the GPX file with any proximity alert distance. Phone number shoud be enteres with leading symbol: >+
This is the recommended line template:
longitude, latitude, Business name, address; city state >+phone
-73.9741766, 40.7567337, The Waldorf Astoria, 301 Park Avenue; Manhattan; New York City >+212 355 3000
Try to enter few test lines and you'll see how easy it is to use POI editor for Garmin...