I purchased a Sierra Wireless AirCard 595U on Monday night. Plugged it in to my MacPowerbook 2.4 with OS X 10.5 and it Just Worked (tm). I have had one oddity where the wireless connection would connect then diconnect 4 seconds later. I rebooted my system and it has been fine since. Color me happy, so far. PS You might want to check out http://www.evdoforums.com for more information. Colin
I can confirm that Sierra Wireless AirCard 597E (PC Express) card and software that comes with it work fine on a Mac Book Pro running Mac OS 10.5 (i.e. Leopard). There have been one crash of the software on the first day, but it has been working flawlessly since.