hello mr. i am a Voip engineer with more than 8 year of expertise in the field, i have good knowledge of what you need to filter your calls supporting g729 codec and very suitable for you current situation, this will need a dedicated server or vps to work on and will be just an implementation of it, you will be able to filter calls just by pointing your originators and terminator between the system and it will handle it. if you want to talk about this just hit me on chat or on skype: montana3601, best regards.!!