Every VoIP phone contains one or more codecs, and during call establishment, they share their lists of supported codecs. One phone, for example, may say “Hey stranger, I can support codecs A, B, or C”, and the other one will respond “Nice to meet you, I can support codecs “B, C, or D.” At this point, both phones recognize that they could converse in either B or C (this process is can easily be compared to two multilingual strangers meeting on the street, figuring out what languages they share, then deciding which of the shared languages to proceed in).
Depending on how they have been set to prioritize various parameters, one phone may then say “well, since C gives better audio bandwidth than B, let’s proceed with that,” or “B uses a lower bit rate and my company thinks that’s more important, so let’s proceed with that.” In lesser terms, the HDX 7000 Codec is responsible for orchestrating VoIP connection by being the medium between phones. Most VoIP phones contain a number of different codecs covering a range of performance levels, and often, bandwidths.
Having wideband capability does not necessarily mean that a phone is unable to connect to a narrowband phone, it just means it has a wider repertoire and can do both. This can be most easily compared to a musician who is able to play multiple instruments. The HDX 7000 codec, without getting extensively into specifications, has a high audio quality and latency due to extensive codecs.
