These days, there are a few broad services available to get a smooth Internet connection between your home and office.  Getting an acceptable voice quality phone system that works all the time is still a big challenge.  You can try the broadband services offered by Worldlink, Subisu or Mercantile -- there are other companies that provide these services as well.  From my knowledge of the marketplace, Subisu is the most reliable, but more expensive.  Just be sure to tell them you are interested in their interent service because they often talk about their intercity fiber (which is excellent).  Irrespective of your choice, my suggestion is that you try to talk to a senior staff member before making a final selection so that you can get expedited support through that person if necessary.

If you are traveling from the States, where broadband ubiquitous and affordable, the prices in Kathmandu might startle you. 

ISPs don't provide VOIP solutions yet (as of Dec 2007).  A vonage system, skype, or other VOIP solutions including the ones that are integrated with your PC will work.  However, getting it to a level acceptable for business is still a challenge.