Yes, however you have to change the default Exchange voicemail storage compression codec from WMA format to WAV for now. I have heard Blackberry is working on changing this at some point.
What storage codec options do I have for UM voicemails?
In general, UM supports three different storage compression codecs, including G.711 PCM (*.wav), GSM 6.1 (*.wav) and wma (*.wma). In terms of file size, G.711 PCM gives you best quality but largest size, GSM 6.1 is almost the same as WMA but lower audio quality. You can find out more here (http://technet.microsoft.com/en-us/library/aa998670.aspx). Keep in mind sizes of voicemails will increase with moving away from WMA (11k for 10 sec for WMA, 160k for 10 sec with G.711 and 16k for 10 sec with GSM)
Can I mix and match storage codecs in the same dialplan?
Yes, can either set GSM to apply to all the users in the dialplan or if you have a small subset of Blackberry users, you change just those users to WAV (GSM) and leave the rest as WMA. Using the Exchange shell you can change it like this for example:
Set-UMMailbox mailboxalias –CallAnsweringAudioCodec GSM
More on the command options here.
Just a side note from a TCO perspective, a research company released a study where there is a 20-28% reduction in the TCO when moving to native Exchange ActiveSync (Windows Mobile/iPhone support) from Blackberry Enterprise Server.