It turns out that this is 100% possible, although a bit hacked.
If you want it to work on Android, you need to use this format:
<a href="sms:/* phone number here */?body=/* body text here */">Link</a>
If you want it to work on iOS, you need the following:
<a href="sms:/* phone number here */;body=/* body text here */">Link</a>
Live demo here: http://bradorego.com/test/sms.html (note that "Phone and" body "and" Phone and body "should autocomplete as a field: and body text. View source for additional information)
UPDATE:
Obviously, iOS8 had to go and change things for us, so thanks to some other commentators / respondents, a new style for iOS appeared:
<a href="sms:/* phone number here */&body=/* body text here */">Link</a>
(phone number is optional)
Bradley Orego Oct 01 '13 at 21:32 2013-10-01 21:32
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