How many phone lines support and in what countries? The telephone lines are one thing and incoming numbers (DID´s) are another, though both are unlimited.
Do these support Venezuelan telephone lines? Sure there are dozens of vendors worldwide DIDs. Here´s one we´re sure they work. http://www.didww.com/
If the telephone line I have is VOIP, can be configured for the server channel calls? If you have access to the user and passwords of the phone line that you have you can try loading the server, but these lines are regularly linked to a type of Internet connection. Venezuelan suppliers regularly only give a pre-configured and locked ATA.
Does this service have a calling rate? There are plenty of installable modules but you should review the Elastix Elastix documentation because the product does not include application-level support.