Well, you already seem to have the application (war-file). This is an
application format that is supposed to run in a web-container. It
probably also means that the application does not utilize a full stack
of j2ee-technologies (ie no ejb's), which makes things a little easier.

Now, you need an application server with a web-container to run the
application. If you don't already have one, I'd recommend Tomcat, which
is the most widely used one. Chances are your app already has been
tested on Tomcat and will run without problems. Download from
tomcat.apache.org if you don't have it already (or you intend to run the
app at a web-hotel with java support)

It is quite likely that the application needs a database to store data.
Part of installing the application in the application server (a process
called deployment), would then be to configure the database (create
tables etc.). Some web-applications does this by themselves, as soon as
they're given connection data (database host,username,password etc.),
others require you to do this manually or by running supplied sql scripts.

Finally it seems your application will need some sort of gateway to a
phone system. Setting up the connection here will likely require some
configuration steps, just like setting up the database. Exactly what
this involves is impossible to say...

I have no idea where you've gotten your application, but specific
instructions on how to install, configure and run should be available at
the same source. Also, war-files are basically zip-archives with a
specific file-structure inside. You can try to unzip and look for files
like *.xml and *.properties that may hold configuration data. Also maybe
(hopefully) you'll find some documentation inside the archive, look for
*.html, README, *.pdf etc.