I've gotten it to work by creating the following policy:
access-list 100 line 1 extended permit udp any any range 10000 49999
class-map sip_audio_port
match access-list 100
policy-map sip_policy
class sip_audio_port
inspect sip
service-policy sip_policy interface inside
service-policy sip_policy interface VOICE
Why should I have to specify the high range when SIP is enabled by default for the inspect policy? The inspect policy for SIP should know how to open up these high ports automatically.