Newbie help: Can asterisk help me share a single number between multiple handsets?

Apologies if this is a dumb question, but I have a specific, hopefully simple thing I want to do and no idea where to begin looking.

I have a single VoIP line provided by my ISP (Internode, and their voip service is called NodePhone, in case that helps). They gave me a username/number, password, and a domain name to put into my VoIP device of choice. This is the extent of my VoIP knowledge, and the extent of the support they provide.

I’ve plugged those settings into a VoIP app on my smart phone, and it works. Tried the same details in Linphone on my PC, and they work. However, I can’t use both at the same time.

What I want is for any incoming call to make all connected ‘handsets’ ring, with the option to pick any of them up. Assuming the line is not in use, I would like to be able to make calls from any handset. I have no need to be able to call one handset from another. I have no idea if making multiple calls from my VoIP service is possible, and while that might be nice, I don’t really need it.

Can Asterisk help me do this? If so, can you point me in the general direction of how to do this? Alternately, if I am attempting to swat a fly with a Volkswagen here, is there simpler way to do what I’m trying to do that you can point me towards?

Don’t use the extension number as a device name (its bad from a security point of view anyway).

Your dialplan for the context from the ITSP should be based on:

exten => s,1,Dial(SIP/<device1-ID>&SIP/<device2-ID>>&......)

Your dialplan for the context containing the internal device should be a standard external calls one.

This assumes the ITSP sends no digits in the SIP INVITE.