I dont know of any amiga programs, but the site me and my friend created should do the job, its address is
http://www.jakkass.com - it allows you to send international texts (if that is currently working) for free.
Plus ive tested the site and it works in iBrowse 2.4 and hopefully AWeb. (I test all my sites in Amiga Browsers!) :-)
Hope that helps!
