After installing Exchange 2007 Standard edition (but luckily not yet migrated many mailboxes)the company has now decided they want to investigate the Unified Messaging. Have put the Enterprise CD in and added the Unified Messaging role and rebooted.Have ran "Get-ExchangeServer | fl name,edition,admindisplayversion" in Powershell, which comes back as Standardstill so assumingI now needto add the licence key for Enterprise. When I highlight the server in "Server Configuration" there is no option to add the key anymore or to amend.Can you upgrade this way? I could not find anything anywhere for this scenario.

You only need Exchange Enterprise Edition for Clustering the Mailbox role Deli

Cheers for the answer. Have upgraded now using Powershell script.

You also need enterprise for more than 5 storage groups/databases, up to 50 maximum. Remember to reset the 50 GB limit softset in the registry of the mailbox server role if you plan on letting your databases to grow more than that size.