I have a question,are both switches/key systems equipped to interface a T-1 circuit. Right off the bat you will need DSU/CSU or a router with a DSU/CSU blade to split the signal, allocating bandwidth for both voice and data. So initially you will need additional equipment. Also the two switches/key systems will need to exchange call processing information or appear as a node or opx (off prem extension) to one another in order to “talk” to one another. A protocol commonly used in this type of application is Q sig. There are workarounds but more information on the telephone systems is needed.