I don't know the built-in 3CX reports well, but perhaps there is a report you could run in 3CX that would allow you to export the data? Naturally, you would need to clean up the data so it would be a manual process.
You have not provided much information about how or why you need to access this information, so I'll take a guess at what you are trying to achieve. Perhaps you are a hosting partner that bills based on the number of extensions configured on the phone system? And you want to query your 3CX servers from a central location to generate client invoices?
There isn't an easy way to do this. You would need to create a web server running on the 3CX server that publishes your own REST API. Under the covers, you would need to connect to the 3CX Call Control API and query the extensions list and return the data via your API.
We have a complete VoIPTools REST API built in to our Relay. One of the APIs returns a list of extensions. But if I have guessed correctly why you want the list, we also are building a tool specifically for hosting partners that will query your 3CX servers from a central application and collect information (including an extension list) and build an invoice for each server. If you have ideas about what information you would like to query, let me know.
