You don't need to buy a licence from Digium if you are just passing g.729 through the pbx i.e. both parties have their own codecs e.g. in the phones or you are going from a phone to a sip carrier that supports g.729.
You only need g.729 if you are encoding or decoding.
I also understand that you can get a developer licence and also a "free to use" version of the codec from intel:
Study or experiment with G.729 for free
Under patent legislation, it is quite legitimate to study or experiment with a patented technology. You only have to pay royalty fees if you sell a product based on the technology, or use the technology in products internally. The free G.729 implementation does not make any changes to Asterisk, so the GPL license is not jeopordised in any way.
It is quite offensive to suggest that a competing product will jeopordise the Asterisk project - Digium is a business, and business is a competitive game. There are many ISDN cards that compete with those sold by Digium, but I don't see anyone being criticised for trying those non-Digium cards. In fact, having competing products available in the marketplace only serves to encourage innovation - and open source is all about making innovations available to everyone.
The G.729 debate on the mailing lists has brought out many opinions, some based on legal grounds, others based purely on personal beliefs. Let's focus our energy on encouraging everyone who makes contributions to Asterisk, innovating, and putting more technology in the hands of more people for less money.
An opensource implementation of G.729 codec can be found at http://www.readytechnology.co.uk/open/i ... 29-g723.1/. It is a wrapper around Intel Integrated Performance Primitives. Please note: You might still have to pay royalty fees to the G.729 patent holders for using their algorithm and to Intel for using their libraries!
I tried to implement the "free" version of g729 and never had success. If I took into account the time that was spent, it was much cheaper to purchase the licenses from digium. Whether you want to discuss legal or ethical issues is something else, but in reality, the licenses are not free, even if you get them from Intel. In fact if you read the docs, in order to legally use the licenses it will cost you much more than if you purchased the licenses from Digium.