You can set up an account with Callcentric.com and get a USA phone number. They are now able to send and receive texts on your phone - inside the USA. If you are outside the USA, you'd have to log in to Callcentric's dashboard on your computer (or however you access the Internat), and could send and receive SMS messages there.
I pay about $2.95 a month to have the number, and can set it to forward to my UK number or voicemail, as I choose. If it goes to voicemail, I have it set to send me an email to let me know. They say they are working on getting international SMS messages, but that service is not yet available.
Have had this company for years, never had a problem with them. Hope this helps!