This phone is really great if you are learning Asterisk and want to test most of the features. It has many advanced features for a really low price. You can easily find the GXP2000 for around $85 at many online stores.
The first time I encountered this phone was at a clients site. The clients setup was done by someone who decided try their hand at VOIP. From my understanding they decided it was not worth the trouble and took a job in the Bahamas (idiots get all the breaks).
The client had numerous issues regarding dropped calls, echo, static/pop sounds, and general inconsistency with dialing certain numbers.
Many of the issues were to do with just sloppy configuring on the initial setup.
The only items that I could not fix were the static/pop sounds - I found it strange since all the phones were GXP2000 but only some of them were causing problems. A firmware update did not fix the problem phones.
I later purchased one of these phones for my own personal use and testing. I updated the firmware and used it for several months. To my surprise everything worked great. No pop or static sounds and even the speaker phone worked well.
My initial thought was that Grandstream fixed everything with a new firmware. At this point I thought this was is not a bad entry level phone for some clients looking to save some money. Even recommended the product when someone would ask.
Over time I figured out what the main problems were with the GXP2000:
1. Different versions of hardware - the more recent versions support an additional green LED instead of just a red LED for the line and speed dials buttons. The newer phones come with 2.5mm headset jack - the older ones come with bigger jack and 2.5mm adapter.
2. The speaker phone quality greatly varies from different batches. I have used versions which sounded great and other that were terrible
3. General quality is bad - over time these phones have a high failure rate. They will develop various problems. One issue is the static/pop sounds and the other is the "buzz" which comes and goes.
4. If the phone is configured to be a remote extension and at some point the phone is brought into the office and simply plugged into the local network it create all kinds of havoc on the call quality of the other phones. You need to do a "sip show peers "in asterisk command console. Look for any phones that have an IP address that points to the router (you need to fix those)