I found the following which may help you:
https://www.rfc-editor.org/rfc/rfc5724
You can check sub-section 2.5 or 2.6 of this RFC to give you some additional pointers on formulating a proper SMS URL.
Eg. using formal URI-spec as detailed in sub-section 2.2 of rfc5724:
<a href="sms:+19725551212?body=hello%20there">SMS Me</a>
Notice the ‘escaped’ character for the ‘space’ in the example above.
Hopefully the Android browser will permit you to generate XHTML forms based on this syntax. I believe they will (if I have some time over the next day, I shall give it a try on my Galaxy S).