...Or until the potential new report is available you could use something like CallSequitur which analyses your calls using the CDRs that can optionally be produced by 3CX. This will give you a live updating chart of the SIM call level (and more...), for example:
As @Saqqara mentioned, for now you can enable email notifications for when the License Limit is reached under Settings >> Email >> Notifications >> License Limit is reached. Whenever the max allowed sim call is reached, an email notification will be sent to the administrator email address of the 3CX PBX (email configured under Settings >> Email >> Notifications).
You could also keep an eye on the "Number of Calls in use" counter in the Dashboard >> under PBX Status, for a live view of the sim calls at any given moment.