From VoIP.ms Wiki
Short Message Service (SMS)this feature introduced on 2013 will allow you to send and receive messages with your DID Number (US DID Numbers Only).Currently is in beta and will remain free throughout 2013 (the price will be 1 cent per message starting in 2014).
Please note that this feature is for regular customer usage. No automation, telemarketing, bulk sending or receiving will be allowed.
The first you need to know is that this feature is only available for US DID Numbers at this moment, also you will encounter that some numbers will have now a little icon of a phone device, this has been deployed to indicate that the number support SMS.
You can start ordering a DID Number from your portal >> DID Numbers >> Order DID >> Local Numbers >> US Numbers and you will be able to purchase your desired number, just make sure it support the SMS feature.