Hello,
suitecrm doesnt come with SMS functionality.
If you are a developer you can customize the phone filed to have icon and then use the API integration with the service provider of your choice.
There are some integration already available in SuiteCRM store You may check.
Many SMS providers have a system that allow you to send an email to them, and they convert it to an SMS to a specified destination. This does not require any complexity on the SuiteCRM side, you can just send email.