The following classes are available as a part of the SIP Client API:
CSIP, CSIPClientTransaction, CSIPConnection, CSIPDialog, CSIPDialogAssocBase, CSIPInviteDialogAssoc, CSIPMessageElements, CSIPNotifyDialogAssoc, CSIPreferDialogAssoc, CSIPRefresh, CSIPRegistrationBinding, CSIPRequestElements, CSIPResponseElements, CSIPServerTransaction, CSIPSubscribeDialogAssoc, CSIPTransactionBase, CSIPHttpDigest, MSIPConnectionObserver, MSIPHttpDigestChallengeObserver, MSIPHttpDigestChallengeObserver2, MSIPObserver, MSIPRegistrationContext.