Codecs for Europe: a-law/alaw/malaw/g711a/711a and for USA: u-law/ulaw/mulaw/711u/g711u. Never use the “u” version.
Many phones have by default ulaw selected, this seriously degrades voice quality. As well it uses a large amount of CPU cycles.
g729a is a licensed codec with low bandwidth use. This is supported in the AOX but requires additional licensing.
Please contact us department if you have any further questions.