I suggest seperating them. Make life easier. If they are on the same router, and your router goes down, you lost both voice and data. If they are on seperate routers, and one goes down, you only lost 1 of the 2.
It is what it is!!
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A+, Net+, I-Net+, Certified Web Master, MCP, MCSA, MCSE, CCNA, CCDA, and few others (I got bored one day)