Question : Asterix VoIP Connection

We are interested in implementing a VoIP telephone switch for a business with a site of 400-500 telephones.

I see plenty of information on how to connect the VoIP switch via an older (and expensive) ISDN30 type connection, but i'm confused as to how we might route all calls out to the internet via a 10MBPS leased line internet connection instead.

I'm guessing there are providers which will take and route calls to and from our VoIP switch via the internet? But i cannot find much information on that.

I would much rather move from the ISDN30 connection to an internet connection to make things easier to support etc. (plus i think it would be much cheaper and have more redundancy, if done correctly)

Does anyone have experience of doing this? i.e. 400-500 DDIs via a service provider into an Asterix PBX over a 10MBPS internet connection. (i would imagine only ever 30 calls at any one time)

Even better if you have experience on using a 3G/GSM card as a backup.... i think this would be a really slick solution.

Do you know of any service providers who can provide this service? (will BT??)

Or did i get this all confused? : )

Many Thanks In Advance

Answer : Asterix VoIP Connection

You have two solutions here, first drop the ISDN and to migrate all your DID to a good sip provider, you will need ate least 22mb uplink to them.
Second is to keep the ISDN lines, use them only for receiveing the calls, and use sip for outbound only.
Now go get your bills, and check how much your isdn lines cost without dialing out with them.

How much would cost the same amount of minutes by sip provider. Calculate the money saved.
And now when you got numbers in place ask yourself is it worth to go all sip ?

Now have you considered to go with something else then naked asterisk ? The cummunity does not help when you got 500 peoples unable to call. In your place i would go with something like trixbox pro and their hud software.