Like you said a router would be the solution to segment broadcast domains.  Once you connect the 2 devices then they forward all broadcast.  You may be able to set up an ACL to allow on the MAC address of the workstation across the connection on an interface.  Starting on page 276 of the 35XX User Guide below discusses ACL configuration. support.dell.com/.../en_ug.pdf Starting on page 323 of the 55XX User Guide below discusses ACL configuration support.dell.com/.../en_ug.pdf Basically you would put an ACL on the interface that you are connecting with the cat 5 that would permit the mac address of the workstation into the 3524P.  Then a similar ACL on the port of the 5548 permitting the mac of the VOIP server to allow a response back from the server.  At the end of every ACL is an implicit deny statement.  This would block everything else and only allow what you have specified in the statement.  This would allow any traffic originating from the VOIP server to cross over to the 5548. This option may be a little tricky to set up.  It is also not a 100% answer.  It is an option thou. Hope this helps, Keep us updated if you can.
I have two Dell PowerConnect switches. A 5548 that services all our computers and servers, and a 3524P that services all our VOIP traffic. I'd like to be able to RDP into the VOIP server from a computer on the 5548's side of the network. If I wanted to connect the two switches together with just a regular CAT5e cable, is there an easy way to ensure that they are not passing any data between each other? The only thing I want is to be able to connect to that VOIP server through RDP. All broadcasts should not traverse the switches. I know I could do this if I put a router between them but I was hoping to avoid that.
Blocking broadcasts