I don't see any official model numbers on the cabinets. I decided to take some pictures of the main cabinets, hoping they might help.

Voicemail - we originally had only 4 lines, which easily got tied up and folks were getting busy signals a lot. We bumped that up to 12 lines, and the busy signal problem has been resolved.
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Inside the main cabinet

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Network card in main cabinet

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Side of Main Cabinet

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Inside Expansion Cabinet

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Side of Expansion Cabinet

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