Thanks to hdawg for pointing me to this KB at RIM (not much new except for the DTIM setting):
BlackBerry Search Results
Recommended settings for the Wi-Fi network when using UMA voice service
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Doc ID : KB14461
Last Modified : 2007-12-13
Document Type : What Is
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Environment
BlackBerry® 8820 smartphone
BlackBerry® Curvexxx8482; 8320 smartphone
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Details
To optimize the Unlicensed Mobile Access (UMA) voice service on a Wi-Fi® enabled BlackBerry smartphone, the following settings are recommended on the Wi-Fi network:
Configure all access points for Delivery Traffic Indication Map (DTIM) to 2.
Turn on Wireless MultiMedia (WMM) and make sure that voice traffic is prioritized (that is, the UMA voice traffic is marked and it is prioritized over the wireless local area network (WLAN) link).
Make sure the latest firmware update for the wireless router is applied from the vendor.