Spectralink does support 40 &128 bit WEP. I am not aware of any known problems configuring WEP on the phone. – Maybe someone else can help???
Be aware the Spectralink phones only operate at 1Mbps and 2Mbps rates so the AP needs to have these rates enabled.
Its also recommended that Aironet extensions are turned off on the AP, and that the AP is configured to "long" Radio Preamble.
The Spectralink supports QOS from the phone (proprietary implementation). The AP will automatically prioritize SVP traffic to the phone.
Spectralink voice traffic is also easily identified in the network (IP protocol 119) and is always destined to the Spectralink gateway. This is important because of the relatively low level of security static WEP provides; you are able to set filters that only allow IPSEC traffic for VPN clients and SVP, TFTP, DHCP, and DNS traffic for phones. With other vendors you cannot do any port filtering because you cannot identify in advance what ports RTP traffic will use.
