Slow aironet 350 series?

Hi, anyone ever had any problem with the 350 series aironet being a bit too slow and distorting phone calls over it? We've got something like 3 analogue phones and 3 computer terminals hanging off the aironet, which should be able to do this easily. Signal strength is good, any idea's on why this could be?!?

Could there be other wireless networks within range on the same or adjacent channel that are blocking you. Or interference from some external source?

QoS Should be configured. Here is an example with an Cisco 1200ap it will be different for a 350 tho.

class-map match-all _class_AvayaIPPhones0
match ip protocol 119
!
!
policy-map AvayaIPPhones
class _class_AvayaIPPhones0
set cos 6

Also Id like to add to get any "real" qos with voice over wireless you need to purchase a spectralink SVP010 they are about 500 bucks but they work great for our wireless Ip phones.