if the selection corresponds to the first entry, executing {HEAD ~ a set} of {TAIL ~ voice exchange operations} to initiate the voice exchange session using a value of the first entry; and 
of
if the selection corresponds to the first entry , executing { HEAD ~ a set } of { TAIL ~ voice exchange operations } to initiate the voice exchange session using a value of the first entry ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH