Personally I enjoyed high-school. Got some of my best sleep there.

But as Aircom said, VoIP (much like TDM) requires someone who knows what they are doing.

As far as advantages or disadvantages of VoIP vs TDM you can search this board to your hearts content to find that info out.

What you probably wont find much on is hosted VoIP. So I'll list what I can think of for it's advantages and disadvantages.

Advantages:
- Better Infrastructure (sitting in colo usually)
- Cheaper access to bulk lines (50+ phone lines)
- Should have better SLA (Colo can have redundant power grids, large-scale battery back-up with genpower, multiple Tier-1/Tier-2 bandwidth mix, etc)
- Should be able to handle larger number of distributed users with less issues
- Usually less vulnerable to storms and other things related to acts of god
- Usually maintained with back-up's and can quickly recover (should be within hours) from hardware failures
- Usually can offer interesting phone routing options in case of last-mile failure or what-not
- Hopefully cheaper long distance thanks to bulk-rate/carrier pricing

Disadvantages:
- High-Quality internet required for any sort of office locations (SDSL, T1, MPLS, etc) with multiple phones; Single-phones should be OK but your mileage may vary
- Cost more for brick-and-mortar offices (non-distributed phones)
- Not cost effective for smaller set-up's (sub 50-trunks I guess)
- It's a service; If the company you are with goes belly up or decides they no longer want your business you have to start over from scratch.

That's kind of what I can think of that relates specifically to Hosted VoIP vs In-House VoIP or TDM.

For a lot of lengthy (sometimes heated) discussions of VoIP vs TDM in general feel free to use the search function of this board. There was also a nice write-up by Ed that is stickied at the top of this forum as well.