This first log excerpt is when I boot into a linux kernel that has the zaptel drivers installed, this results in asterisk not being able to play sound to me, so I can't hear the vm-login recording.
Aug 26 15:58:18 DEBUG[2856]: Setting NAT on RTP to 0
Aug 26 15:58:18 DEBUG[2856]: Stopping retransmission on '5a108cbb-4ad81ef5-bf876d0a@192.168.3.201' of Response 1: Found
Aug 26 15:58:18 DEBUG[2856]: Setting NAT on RTP to 0
Aug 26 15:58:18 DEBUG[2856]: Check for res for 201
Aug 26 15:58:18 DEBUG[2856]: Call from user '201' is 1 out of 0
Aug 26 15:58:18 DEBUG[2856]: build_route: Contact hop: <sip:201@192.168.3.201>
Aug 26 15:58:18 VERBOSE[2856]:     -- Executing Answer("SIP/201-ec07", "") in new stack
Aug 26 15:58:18 VERBOSE[2856]:     -- Executing Wait("SIP/201-ec07", "1") in new stack
Aug 26 15:58:18 DEBUG[2856]: Stopping retransmission on '5a108cbb-4ad81ef5-bf876d0a@192.168.3.201' of Response 2: Found
Aug 26 15:58:19 VERBOSE[2856]:     -- Executing VoiceMailMain("SIP/201-ec07", "default") in new stack
Aug 26 15:58:19 DEBUG[2856]: Ooh, format changed from unknown to ulaw
Aug 26 15:58:19 DEBUG[2856]: Scheduling timer at 160 sample intervals
Aug 26 15:58:19 VERBOSE[2856]:     -- Playing 'vm-login' (language 'en')

This next excerpt is from a different kernel on the same box that doesn't have the zaptel driver compiled, here the sound works find, and I can here the vm-login recording:
Aug 26 16:07:05 DEBUG[2820]: Manager received command 'Command'
Aug 26 16:07:05 DEBUG[2820]: Manager received command 'Command'
Aug 26 16:07:31 DEBUG[2820]: Setting NAT on RTP to 0
Aug 26 16:07:31 DEBUG[2820]: Stopping retransmission on '4b8b0eed-75aefca3-36ccacb8@192.168.3.205' of Response 1: Found
Aug 26 16:07:31 DEBUG[2820]: Setting NAT on RTP to 0
Aug 26 16:07:31 DEBUG[2820]: Check for res for 205
Aug 26 16:07:31 DEBUG[2820]: Call from user '205' is 1 out of 0
Aug 26 16:07:31 DEBUG[2820]: build_route: Contact hop: <sip:205@192.168.3.205:5060>
Aug 26 16:07:31 VERBOSE[2820]:     -- Executing Answer("SIP/205-6859", "") in new stack
Aug 26 16:07:31 VERBOSE[2820]:     -- Executing Wait("SIP/205-6859", "1") in new stack
Aug 26 16:07:31 DEBUG[2820]: Stopping retransmission on '4b8b0eed-75aefca3-36ccacb8@192.168.3.205' of Response 2: Found
Aug 26 16:07:32 VERBOSE[2820]:     -- Executing VoiceMailMain("SIP/205-6859", "default") in new stack
Aug 26 16:07:32 DEBUG[2820]: Ooh, format changed from unknown to ulaw
Aug 26 16:07:32 VERBOSE[2820]:     -- Playing 'vm-login' (language 'en')
Aug 26 16:07:35 WARNING[2820]: Couldn't read username
Aug 26 16:07:35 VERBOSE[2820]:   == Spawn extension (from-internal, *98, 3) exited non-zero on 'SIP/205-6859'
Aug 26 16:07:35 VERBOSE[2820]:     -- Executing Macro("SIP/205-6859", "hangupcall") in new stack
Aug 26 16:07:35 VERBOSE[2820]:     -- Executing ResetCDR("SIP/205-6859", "w") in new stack
Aug 26 16:07:35 DEBUG[2820]: cdr_mysql: inserting a CDR record.
Aug 26 16:07:35 DEBUG[2820]: cdr_mysql: SQL command as follows:  INSERT INTO cdr (calldate,clid,src,dst,dcontext,channel,dstchannel,lastapp,lastdata,duration,
billsec,disposition,amaflags,accountcode) VALUES ('2005-08-26 16:07:31','\"205Poly500\" <205>','205','*98','from-internal', 'SIP/205-6859','','ResetCDR','w',4
,4,'ANSWERED',3,'')
Aug 26 16:07:35 VERBOSE[2820]:     -- Executing NoCDR("SIP/205-6859", "") in new stack
Aug 26 16:07:35 WARNING[2820]: CDR on channel 'SIP/205-6859' not posted
Aug 26 16:07:35 WARNING[2820]: CDR on channel 'SIP/205-6859' lacks end
Aug 26 16:07:35 VERBOSE[2820]:     -- Executing Wait("SIP/205-6859", "5") in new stack
Aug 26 16:07:35 VERBOSE[2820]:   == Spawn extension (macro-hangupcall, s, 3) exited non-zero on 'SIP/205-6859' in macro 'hangupcall'
Aug 26 16:07:35 VERBOSE[2820]:   == Spawn extension (from-internal, h, 1) exited non-zero on 'SIP/205-6859'
Aug 26 16:07:35 DEBUG[2820]: update_user_counter(205) - decrement inUse counter

Why would the zaptel drivers effeect this?