Asterisk

Benefits:

Asterisk is a free and open source voice over IP system. It removes the need for purchasing expensive hardware. There is a large community of users around the world that will help troubleshoot and setup.

Drawbacks:

It can be hard to setup and implement at first as the company support is not the best either.

Benefits:

The openness of the system and ability to create so many solutions based on this little piece of software. It is a great foundation for creating a telecommunication solution for yourself.

Drawbacks:

If creating apps using Asterisk you need to know deep knowledge of the solution, this is a software that is for skilled people to use and create, which is not bad, it is just what you have to expect.

In sum:

Really good, I've seen several deployments of Asterisks and they work smooth silk.

Benefits:

Asterisk is a reference in its domain. OpenSource, free, a lot of features. It became an industry standard and provide certification and a real user support / community support

Drawbacks:

You need to know what you are doing, probably not easy to start.

Benefits:

Full functioned Millions of deployments Large community to help with problems or configuring it

Drawbacks:

Need to be careful not to leave it open to fraudulent calls As a CLI based tool it can be a bit confusing to install from the tgz

Benefits:

I like that this software can be used for video conferences, automatic call distribution and it can be sustained on VoIP. It has been really useful over the years.

Drawbacks:

I don't have any complain on it. This has been an amazing software so far.

In sum:

We have an organization with 1000 employees and Asterisk have been great for connecting all the offices. We have used it for years and it is a very reliable software.

Benefits:

The phone system has a lot of features and functionality which allows us to do much more than our previous phone system. It let's setup IVR's, voicemails, call routing and other features that our old phone system did not support.

Drawbacks:

Our hardware has had some durability issues and we have had to replace some even though our system was not very old.

In sum:

We haven't experience any problems on the Digium PRI Card that we procured 2 years ago. The accessory is easy to install and set-up. It is also compatible on any PBX Solution Software.

Benefits:

Very customizable product. Multiple codecs support. IAX2 protocol is a free way to save bandwidth. Free software.

Drawbacks:

Not accessible to anybody, requires basic Linux knowledge. Many releases with minor bugs, you have to find and test the good one for your needs.

In sum:

Very convenient if used with a graphical web interface like FreePBX. It is definitely a good product if you bundle with other tools.

Benefits:

Open source code, available in to many versions, constant upgrading for the comunity, perfect SIP adaptable configurations, to many features and modules.

Drawbacks:

Hard installation and configuration, some bugs are not resolved at all in sip trunking, codec, an others, at least to the version 11, but now on the version 13+ there are more good stuff

In sum:

All my voip implementations are based on asterisk as well

In sum:

If you want a good and free open source VOIP solution that you can manage in house, then Asterisk is a good choice. It can be easily installed (not upgraded however) and managed by IT system administrators. Is logic (queues, SIP opening and context for calling) is something that you will figure out quite quickly. You can even use multiple WAN ports and multiple SIP trunk operators with the same server so this is also an advantage. The biggest disadvantage is that if a new version comes out it is easier to do the fresh installation then rater to go and try to make an upgrade. Overall, as an open source system it is a great value for money.