Got it working - Thanks! Also some tips/updates
Thanks a lot, I got everything working. Free phone system until 2014 and I learned some things along the way! Nice
For reference here is my configuration:
* Amazon EC2 t1.micro instance w/ Ubuntu, Linux kernel 3.2.0
* Asterisk 11.3.0
* Google Voice account currently associated with old cancelled landline
* SIP clients used: Twinkle, Ekiga, 3CXPhone for iPhone
One tip - I don't think you need to compile a new kernel yourself to get 1000HZ timing - instead you can install the premade "low latency" kernel which already has this setting ("apt-get install linux-lowlatency"). You need to manually edit /boot/grub/menu.lst so that the first/default entry refers to the new lowlatency kernel.
It also seemed like I could effectively control the 1:1 NAT firewall settings from the EC2 web console and provide adequate security without bothering to configure ufw, although I can see how it might be better to properly configure that too.
One problem I had is that I was getting "Illegal Instruction" errors from Asterisk and it would crash. What was going on is that Asterisk was being compiled to use AVX instructions which GCC thought were supported on the CPU, but the EC2 micro instance did not actually support AVX instructions. I found this is a known issue other people have had with EC2 instances. I worked around it by changing the Asterisk build options ("make menuconfig" / "Compiler Flags") so that "BUILD_NATIVE" was disabled, recompiled and voila, no more crashes!
I still haven't figured out how to make the PPTP VPN work right; with Windows and some other clients it fails to negotiate encryption. I'm sure I'll get that working eventually but meanwhile not too worried about it.
Thanks again to errorcod3 and jhax01 for putting this together!