can anybody tell me what the max noise threshold is for a VoWLAN deployment
For Vocera deployment the badge should have at least -65 dBm RSSI and SNR should be above 25. Refer to Vocera deplyment in Cisco Unified Wireless Network Infrastructure document at http://www.cisco.com/en/US/tech/tk722/tk809/technologies_configuration_example09186a0080766d54.shtml#c5
More information at http://www.vocera.com/downloads/InfrastructureGuide.pdf
Basically you have to ask your VoIP wireless phone vendor for signal related requirements.