1) Welcome to the party!
2) when you post, please post your entire configuration including (but not limited to) your installation method and vicidial version with build.
this IS a requirement for posting along with reading the stickies (at the top of each forum) and the manager's manual (available on EFLO.net, both free and paid versions)
You should also post: Asterisk version, telephony hardware (model number is helpful here), cluster information if you have one, and whether any other software is installed in the box. If your installation method is "from scratch" you must post your operating system and should also post the .iso version from which you installed your original operating system. If your installation is "Hosted" list the site name of the host.
If this is a "Cloud" or "Virtual" server, please note the technology involved along with the version of that techology (ie: VMware Server Version 2.0.2). If it is not, merely stating the Motherboard model # and CPU would be helpful.
Similar to This:
Vicibox X.X from .iso | Vicidial X.X.X-XXX Build XXXXXX-XXXX | Asterisk X.X.X | Single Server | No Digium/Sangoma Hardware | No Extra Software After Installation | Intel DG35EC | Core2Quad Q6600
While I realize that you believe you are asking a "general question", it is entirely possible that the version of the software you are using Has a feature or Does Not have a feature simply by virtue of your version. The same applies to your installer. In this case, of course, it does not. LOL
3) AMD (Answering machine detection) is free, and fatally flawed. It also has not changed in years. It is roughly 70% accurate by the best estimates I've experienced and heard of. That means 30 of 100 humans are treated as Machines and 30 of 100 machines are treated as Humans. Not a good thing. We've experienced up to 85% accuracy by "playing with it" (changing the configuration files), but this is not a guarantee, usually 80-85% is the final accuracy range.
Sangoma, on the other hand, seems to be much better at it. I will not state specific %ages because there are several posts already and they are not Mine (whereas the above experience IS). Sangoma, of course, is also Not Free. They DO have a "teaser" trial (allowing for 1 channel use to test the system).
4) Summary: Read up on this forum of the experience of others (it's already here, you just need to search for it) and post YOUR results if you make the purchase! (and always post your specs for your system to get the best response from this forum!)