Please ensure that you have purchased your account with the Mobile Communications feature. To verify this please follow the below mentioned steps:

1.Click on the Admin button from the header and choose Admin option from the list.
2.Click on the Account Summary tab.
3.Verify if Yes is displayed in the Mobile Communications(Chat & SMS)  field in the license info section.
4.If not purchase the Mobile Communiations feature using the Plan - Addon's button.