When activating from a evaluation EULA, EBS is activated the same as Windows Server. 

To enter in the key all you need to do is;

1. Make sure you have the keys for EBS.  You should have one for each Server role, Management, Messaging and Security.  You’ll also need CALs either device or user CALs to suit your organization.
2. Ensure you have your internet connection correctly setup

Click Start

Right Click Computer and select Properties

Next click Change Product Key

Enter your product key for the right server role and click Next

Follow the rest of the prompts to complete the key activation.  Repeat for the other two servers.

Next you’ll want to add your CALs

Start the EBS console and select the Licenses tab

Click Install CAL Packs and run through the Wizard

Finally assign the CALs to the users and devices as required

Thanks Nick for this guidance!!!