If you do your survey right, tune RRM, have all the phones staticly connected on the 802.11a only with the latest software release and QoS is end-to-end in place, you will be fine.
Carefully choose your AirOS release, I did have some issues with one-way audio before the 7.4.121 release. In one deployment I even used WPA2 AES with PSK's but did not experienced issues do to bug CSCtt38270.
If you follow these best practices & use your branch office AP in FlexConnect AP group & CCKM enable on the WLAN you should be fine. In FexConect mode still layer 3 roaming of local switched WLAN is not supported. Below is the latest 8.0 WLC config guide with respect to FlexConnect
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
This is the start of a display filter cross reference between Wireshark
and OmniPeek. The 1st installment is a table of advanced filters. More
filters will be added as time allows. It is a living doc, so check back
for changes every so often Please feel f...