Although the United states remains far behind Europe in terms of overall SMS usage, the networks here are already vulnerable to the equivalent of SMS "flooding" which could overwhelm networks, causing service disruptions - a vulnerability that would especially be felt by mobile medical services among others.
CNN featured a report based on the research of Dr. Subrahmanyam Karuturi at Penn State University talking about exactly this. The article highlights some vulnerabilites of such services and attempts to serve as a wake up call for providers - asking them to take seriously the human tendancy to exploit weaknesses in any system.