If lockdown menu is used, why not just use kiosk item such as

   dial://12345678   

instead of using intent?

Android Plus profile cannot be applied to Android-Enterprise device. As phone whitelist/blacklist policy is only available in Android Plus,  it is currently not possible to use MobiControl to limit Android-Enterprise Phone to only one number.

What is the brand and model of your device?  What kind of configurations of the phone/agent installation are essential if you are using Android-Plus device agent?

Ah, I thought that may be the case.

The device is the Energizer P490S. We will be deployed large numbers of phones so need to be able to deploy as quickly as possible. I had been testing entering afw#mobicontrol so far and that has worked fine, but was planning to use the staging app once we start deploying. The key for us is to complete the enrolment with as little manual interactions as possible and ideally without having to set up different Google accounts.

For configurations we need to be able to lock down to 1 app from the play store and the dialler. The dialler must only be able to call one number. We will then lock down everything else as much as possible.

I think you should be able to continue to use Android Enterprise and still accomplish your goal by possibly linking to a script instead of the Phone/Dialer application in the lockdown utility. The script could broadcast an ACTION_CALL Intent to a specific phone number. 

Thanks for this suggestion Matt. Would you be able to direct me to any examples of this, I've been playing around with it and not having much luck.

I've been able to use script:// from the lockdown to run the file but either get no action or errors in the logs.

Thanks Raymond, that seems to work ok. I have noticed it's possible to accidentally hit the back button and leave the call running with no way to get back into it, but imagine it should be possible to work around this.

I think this is the easy way to do that, RC is right and if you can put this inside the kiosk maybe you can solve your problem fast.