stcogolin

Greetings,
I am a small hotel/big restaurant owner with a 10 year old sx-200 ML. I now want to add voice mail (mainly for the restaurant admin but could also service the 24 rooms with it) and I would also like unified messaging. The options I have found are:

1.) Upgrading the controller to a sx200 icp.
2.) Keeping the ML and adding a voice mail extension (Mitel Express Messenger, duvoice dv4, cisco unity or other?)

My problem with option 1.) is that I feel it may be overkill for my needs. After all, if I only want to add voice mail and my current system works fine, why change the whole system? How long should I expect my ML to last? If it's good for another ten years, then I don't really need to change the whole controller and would prefer a cheaper standalone voice mail solution. On the other hand, the Express Messenger card seems outdated and is almost as expensive as an upgrade and I don't know if the duvoice and cisco unity are reliable and easily implementable solutions. If anybody wants to offer me some advice, it would be greatly appreciated!