sorry my friend there will not be G729 codecs included in the system. maybe you can go for GSM, codecs as it will require less bandwidth as well and you would be looking for less bandwidth codecs.
G729 will be supported in final release of 3CX V.4 See http://www.3cx.com/forums/categories-1/3cx-phone-system-general-1/version-4-crystal-ball-edit-new-feature-announcement-2663/
G729 will most likely be in the final (not alpha or beta) release of v4 but it will be a PURCHASED codec, the free ones are in the present release of 3CX.