[Asterisk-Users] Inbound numbers question

[Lister Account]

I'm a newbie here.  I have a general question that can help drive how
exactly I'm going to get started.

Say I have a single inbound number (1-800-my-number).

When a call is connected on that number, and another call comes in,
will asterisk answer it, will a call waiting signal be triggered, or
will a busy signal occur?

I'm thinking about this for several reasons.

1) for pbx, I want to make sure all inbound calls are picked up.
2) for conferencing, I want to be able to just give someone a single
number to call every time (for regularly scheduled meetings).

As I understand it with traditional telco equipment, you'd have a t1
or a group of lines, and the inbound call would get answered as long
as there was an open line available.  (it would rotate through the
available lines)

If this is still the case with voip in the asterisk world, does this
mean I'd have to have a set of inbound lines?  And if so, could you
point me to the wiki and call me names, or send a link to
documentation about how to set up this rollover behavior?

The way I'm planning on things is to set up my server in a data center
with high bandwidth availability (all voip, no pots or telco t1). 
Inbound calls will be for voicemail, routed to my landline or cell
phone, or conference calls.

This might sound like a stupid question, but I'm wondering if setting
up asterisk is the way to go, or if I should use a virtual pbx
service/conf. call provider.  I prefer asterisk because I'd have
control over everything (and I'm a geek who is addicted to OSS).  If I
have to maintain 10 or more dial-in numbers at a cost of
$10/month/line, it might not make sense though.  (figuring max conf.
call of 6 visitors, and 2 inbound calls that might be routed to land
lines)