Nokia 8910 Codes
#3370# deactivates the EFR, after the phone has been turned off.
*4720# Activates the Half Rate Codec, after the phone has been turned off. HRC produces poorer voice quality but gives your battery better stand-by times. #4720# Deactivates the Half Rate Codec, after the phone has been turned off.
Enhanced Full Rate will give you much better sound quality when you enable it. The new EFR codec uses the ACELP compression technology. This technology allows for much great voice quality in the same number of bits as the older Full Rate codec. The older technology was called LPC-RPE. Both operate at 13 kilobits, but you take up more space on the network, so they can charge you more. Talk-time is reduced with about 5%
Half Rate will give you poorer voice quality, which gives the service provider the opportunity to have more calls on the network, and you might get a lower charge from them. Will give you 30% longer talk-time.