Great question as since Lake Master was purchased by Johnson Outdoors (Hummingbird) They only support the Hummingbird product. If Humming Bird or a company under the Johnson outdoors umbrella made a hand held GPS that would run their chips it would be the ideal situation. I don’t know??
I currently run a Lowrance H2Oc (hate it hard to read it bright lite and difficult menu compared to others I have used but I’m keeping it till something better comes along.) but run the the Lakemaster chips with Contour Elite software. (Love the chip and software)
I recently downloaded the Navionics USA and Canada app on a Motorola Droid RAZR Maxx. Seems OK but have not used it on the ice yet. Also has many other lakes not mapped on Lakemaster it is a good complement to Lakemaster. I would not recommend relying solely on a phone as they are not water proof and when the battery dies your done (no spare batteries at least with the RAZR Maxx)It would be a good complement to a good handheld.
I too would be interested in a good GPS that would run good lake data software. I actually think the software is more important then the GPS device.