How to organize IP telephony in the office?

Well and if grandmas it is a pity to configure Asterisk in the office.
Costs: the server (although you can use and not particularly powerful machine if the office is small), if there is a city line adapter for the city network, if no — "Base" for 250 rubles a month with more channels or one — Alloincognito (+modem for 1500), but for free.
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For domestic subscribers — or at 2K SIP-backgrounds, or adapters. If the interior VERY much — they say there are some cool solutions...
If the components are normal and in the grid — you can put a USB tube+program.
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To access the city, then you can use the Europhone calls on Megafonovsky numbers — Tifon. For other Russian — pcTel. For long distance — you look at the directions...
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In principle, something from my article podcherpnut — Asterisk, telephony or home for (about)moved user — there is, of course, for "home" use, but the overall logic is close...
I'm thinking about the second part — "Asterisk for business or any office", but you need to find a "victim" for "field testing"! ;)

I worked in the same firm.
There were solved with the help of local Linux administrator and Asterisk.
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Though in our "magic", the country had to sign a paper with the local state structure is that it will be used only for negotiations with clients and not for an alternate telephone channel.

For a given task can give solution for cisk. This option is unlikely to be the cheapest though, I think one of the most stable in the work. And You do such a decision would not run, although, if necessary, will be able to help remotely. Yes, for free.
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To take, better used, the 2811 router ( 2801, but it is not fundamentally cheaper and noticeably weaker in the future). If you get voice bundle take — great, there will already be modules for recoding voices.
New clean 2811, the idea is that you can get for somewhere around $1400 plus remap module for about $500 (up to 16 streams)
How much you can get used, especially if there is a way into eBay, you will not tell.
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On it pour Call Manager Express (nothing complicated, even a few video instructions). License the fairness of this procedure, I did not specify :)
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This gateway to put in the Internet and for him to have IP inbound (and outbound) voice stream from operators. Traffic can be encrypted, if there is a demand and operator support. With online channel, you have to think — maybe we should take separate for that matter — depends on availability in Your particular case.
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If you take E1, then it is about $600 for the module interface to the router. But I don't see the point in taking 30 lines where enough for a dozen.
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Inside users to deliver software Communicator and issue the headset.
If necessary, raise the VPN gateway and put users anywhere — even at home.
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I repeat — this solution may not be the optimal cost, but it is guaranteed to work in the mode of "set it and forget it".

Over iota about IP telephony forget but headaches with intermittent voice, echo and non-working Fax get nothing.

We do not soar a brain to the person. You will help any digital PBX. Which to cling to a SIP provider and make calls around the city. Then buy yourself the incoming number.