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
3) How do you know you are using g729?
4) If you are using unlicensed g729, that command will never work anyway.
5) "The clients don't listen well to my agents" is not extremely descriptive. Sounds like they just don't follow instructions unless that's a language barrier issue in your posting. Are you saying that the volume is too low? Sounds is garbled? Robo-voice? Missing pieces?
6) Your Carrier settings "allow/disallow" will determine your codec. allow=ulaw instead of allow=g729 would change your codec from one to the other ... but I'm not certain you are even using g729 to begin with. Post a bit more detail ... (making sure you're not an amateur, one way to tell is the ability to post details, and if you are an amateur you could be using gsm and not know it! LOL)