non-managed switch connected to PC port on IP phone

[TheCurious]

CM4,G650/S8720, H.323 IP phones - models used are 4610 and 4621, computer network is based on Cisco 3750 switches.
Customer run out of ports in ethernet structured cabling, therefore they connected a cheap, non-managed switch to PC port on IP phone. 4 computers are connected to non-managed switch. This solution worked OK for about half a year, now IP phone restarts if I connect any of PCs to non-managed switch. Problem persists if I use non-managed switch from other vendor. IP phone works OK with a single PC connected directly to PC port.
Any ideas ?

The Curious

 

[telcoguy]

Using those cheap switches will get you in this situations very easily. Avoid where you can.
The better way is to put the PC behind the phone, and do a proper VLAN separation on the 3750.
- Did the customer enable the smartport profiling on the Cisco? The graphical client on the Cisco's will nag about you not having applied smartport profiles.
In most cases that is not needed for any reason. But customers seem to think that is something they should do when asked.
- Did they limit the the number of MAC's manually?
look in the config of the 3750 for : "switchport port-security maximum X" for example.
This limits the number of devices behind the uplink port. (smartroles puts this in)
Another option is the customer made changes to the VLAN assignment manually.
Check if the PC's and phones are getting their IP's from the right Pool.
Just my thoughts without having any specifics.