Hi, there is quite some variety of services that you can use.
I personally used Pinger not so long ago.
www.pinger.comIt requires registration, and I believe you need a USA IP address to register (not sure about this), although this can be easily circumvented by using a VPN/VPS.
The website will give you a Cellphone number and a chat window that you can use to receive and send SMS to USA numbers.
Other alternatives you can use: buy a google voice account from one of the providers that can be found on this same forum. You can also do unlimeted free calls to USA and Canada cellphones.