[Asterisk-Users] What's the best way to combine multiple VOIP lines into a single number?

[Leo Burd]

Hello there,

I'm new to Asterisk and I'm wonder what's the best way to combine multiple 
VOIP lines into a single phone number...

I currently have 4 incoming VOIP lines, each one with a different number. 
Ideally, I would love to provide my customers with a single number for all 
those lines.  Is that possible?  If so, would anyone give me directions or 
send me a dialplan example explaining how to do that?

Thanks in advance,

Leo