ExpressCard 34 add-ins are few and far between, leading a fair few notebook users to question the wisdom of laptop makers who've dropped the PC Card interconnect for the new, faster version. The mobile phone network Vodafone recently shipped a USB-connected HSDPA modem for PC Card-less. Perhaps it should have waited for Novatel' …
SMS on a Mac?
You don't need seperate software to send SMS messages from a Mac via this card, because that functionality is already available, built-in, via the Address Book application which pairs with your own mobile, thus enabling you to send SMS messages from your own number, rather than some anonymous data-card SIM phone number.
All Mac laptops come with bluetooth and have done for years. Anyone with a laptop and a datacard is certainly going to already have a mobile phone, which they can pair to the Mac. Thus the requirement for stand-alone SMS software for Macs to utilise the datacard is completely redundant.
You could argue that the need for a seperate datacard is completely redundant too, given that via bluetooth you could just pair your MacBook with your mobile and access data networks that way, but that's a whole new argument.