Presumably Garmin use the Iridium satphone network?
I thought Avidyne did a deal with meteox.com, but that doesn't show any radar data south of the Alps, and the early MLX770 brochures I saw showed the same missing coverage.
What is the cost structure of the Garmin product? I have repeatedly tried to find this out for the MLX770 but totally without success and even the (few) people I know who have it installed don't know what it costs.
I do know that Iridium data is eye wateringly pricey, partly due to the high /minute cost and partly due to the very very slow data rate of 2400 bits/sec so you pay for a lot of minutes. 2400bps is OK for text, and OK for radar as a background activity but it will be pricey unless Garmin do some kind of a special deal with Iridium.