As of November 2016, Clickatell no longer support Email to SMS for new accounts, only accounts created before that date will be able to use that particular service, so this should not be used for new configurations.
Nervepoint Access Manager can connect with an Email-to-SMS Gateway provider and allow you to use One Time Passwords that are sent to your users mobile phones via SMS. There are a number of companies that provide email to SMS Gateway service this article provides an example using Clickatell to get you started.
Once you have chosen a provider you'll need to perform some configuration for the gateway to correctly forward messages from Access Manager to your users.
If you wish to use Clickatell you'll first need to sign up for a Developer Central account in order to have access to the tools required for providing access to an SMS Gateway.
http://www.clickatell.com/ - International Site
Once your Developer Central account is activated you'll need to create an API, specifically an SMTP API.
Creating the SMTP API provides the receiving gateway for emails from Access Manager, the API will then convert the Emails into SMS and send them to the users. In the details here are the parameters that need to be provided with each message to ensure they handled by our API.