It's for IP telephony. It has performed great.

We build our own servers, or sometimes we download a precompiled Asterisk like FreePBX or Elastix. If the client requires it for a call center and installed on his server, then we go with a custom-build. However, if the client wants 20 to 30 phones and it is a small office, then we go with Grandstream or any other ready-made Asterisk equipment like Digium Switchvox.