While I'm thinking of them, here are a few random tips and tricks I've come across, based on my experiences with two Cisco/Linksys/Sipura devices, the PAP2T adapter and the SPA921 IP Phone.


Multiple three-way conversations
The PAP2T can sustain two three-way conversations (but not in G.729.)

Eliminate echo
The best place for echo cancellation is where the IP system meets the POTS system...in other words, on your provider's end.  If your provider does not do proper echo cancellation, there are still a few things you can try.  I find that later versions of firmware seem to do a better job of handling echo on the Linksys devices I've tried.  Additionally, echo can also be greatly reduced by adjusting FXS Input/Output gain or Handset Input/Output gain.

Don't correct jitter if you don't have it.
If your internet connection does not experience much jitter, (variations in ping times) set your jitter level to low.  This can also reduce echo.  (If your internet connection does however experience lots of jitter, you will have voice quality problems.)

Fix Choppy Voice
One contributor to choppy voice is a RTP Packet Size that is too large.  The default on Linksys/Sipura devices is 0.03; try 0.02 or even 0.01.  An added bonus is that this will decrease latency, that is, the time it takes for what you say to reach the recipient.  In some cases, this can also reduce echo.  (Note that this will increase bandwidth usage slightly.)

QoS really does work...
...but a QoS router can only really limit upload bandwidth.  It has no control over what's coming in, hence the many myths that QoS is a waste of money.  Your ISP may have a QoS feature to limit download bandwidth though.  (Anyone tried something like this?  Let me know how you liked it.)

Disconnect supervision on your PBX
...is a good thing to play with, so that it works properly.  This is a feature that automatically releases the call when the party hangs up.  If it's too sensitive, it will drop calls randomly.

Dropped calls?  Check your router.
For some reason, the D-Link WBR-2310 I was using would randomly block all access to the internet for a short period during the occasional voice call.  In its log, it said SYN FLOOD ATTACK DETECT.  I found several forum posts by people who had a similar problem, but found no solutions.  I ended up swapping the router.  If anyone knows of a solution, please let me know.

Call waiting, and many other features, can be disabled on most VoIP devices
My provider claimed they disabled it, but it kept working, until I found the PAP2T setting.

Forwarding is actually redirecting
If you use your PAP2T to forward a call, your provider does all the work, not your PAP2T.

Forward to Voicemail
Want to forward or transfer a call directly to voicemail?  Have your provider set up a SIP URI or internal extension for your voicemail account.

Forwarding a landline can be tricky
I had Telus forward our landline to our VoIP line before our number was ported.  What I discovered was that it could only forward one call at a time; all other calls would get a busy signal instead of going to the VoIP voicemail.  The Telus technician said it was possible to purchase more forwarding channels.  None of the sales reps seem to know about this though.

In a pinch, you can connect multiple devices to the same account
They'll be able to make as many calls as your provider allows.  Whichever phone rings is whichever one registered most recently.  You can disable registration on some phones to make them outgoing only.  Another solution is to select a provider that allows you to create sub accounts.

And finally: I really, really want an Asterisk box
I can't believe I passed up that $50 Atom system that was on Craigslist...