Be aware of any applications that may be used over the WAN that only support (or are only configured to support) G.711 such as MOH, Unity, CRS, etc. You will either need to congigure these applications to support both codecs, move theses services out to the remote locations, or configure a transcoder. Also, if you are using fax over the WAN, you will want to leave these devices in a G.711 region as this will not work with G.729.
Hope this helps. If so, please rate the post.
Brandon