Callcentric to Callcentric calls support whatever codec you want. Typically both ends need to support or allow it. SIP2SIP to SIP2SIP will work as well.
SIP2SIP to Callcentric should work too, although I've never tried.
But if you're dealing with VoIP providers that allow PSTN interconnection . . . it's not happening. The call hits the PSTN gateway, which only works with G.711u and G.729a usually.
You'll have the same problem with G.722. Both ends need to support it. But if you're making calls to POTS (regular telephones), forget it.