I setup an Azure VM using a gallery image of server 2012 and MSSQL 2012 standard.

Can I purchase a license and cals and install that licence on the VM to eliminate the monthly change for the MSSQL 2012?

If so how do I do this?

Hello,

Did you create a SQL Server virtual machine in Windows Azure?  If so, Microsoft charge for SQL Server running on Virtual Machines by the minute and bill based on total number of minutes when VMs run for a partial hour. These rates already include the hourly rates for Windows Server.

If you bring your own SQL Server license, you would not be charged for SQL Server. You create a Windows Server virtual machine in Windows Azure and then install SQL Server using SQL Server setup: copy all the SQL Server setup or data files to a virtual hard drive (VHD) file on-premises and upload the VHD file to Windows Azure by using the CSUpload utility - the Add-Disk option.

Reference:SQL Server Deployment in Windows Azure Virtual Machines

Regards,
Fanny Liu