[Asterisk-Users] debugging voice quality issues

[snacktime]

My * box is connected to our office dsl.  I have an 800# with livevoip
and a sipura spa-2000 on our local office network.  Our livevoip
connection is using SIP/gsm and the sipura is configured for g726-16.

The 800 extension just plays a couple of gsm sounds files and then
goes to voice mail.

When I call an extension via the sipura on the local network the sound
is perfect, which I would expect.  When I call the 800# via a regular
landline I get a lot of static.  I've also had regular static on
similar voice calls going into a couple of other test boxes I have
setup during the last week or so.

Where should I start looking to find the cause of the static?  Is this
just normal for voip?