Methods and apparatus for transparently switching a local instance of a UMTS protocol-based call from a first card or module of a media gateway to a second card or module of the media gateway, such that the remote end of the call is not aware that the call has been switched between the first and second cards or modules. Moreover, initially establishing call media flow may include implementing two timers of different duration during which call-initialization is retried if no Positive-Acknowledgement of call initialization is received, where a shorter-duration timer is relied upon to attempt retries if a Negative-Acknowledgement is received, and a longer-duration timer is relied upon to attempt retries if neither a Positive-Acknowledgement nor a Negative-Acknowledgement is received.