I am running astlinux 0.4.0 on the Soekris net4801 SBC with a Geode class CPU running at 266MHZ and 128 MB RAM. Astlinux uses the Centos (RHEL) base packages with Asterisk 1.2.7. It is extremely light-weight …the whole distro runs into 26 MB without the optional extras. The extras are another 10-12 MB. Astlinux runs off a bootable CF card. All asterisk config files and the user voicemail are stored on a USB stick plugged into a USB port on the SBC. The SBC has three in-built ethernet ports, of which you use eth0 as your main (and only) port to connect to your LAN or WAN. There is only one PCI slot, but I think it supports only 5V cards, I think. I would advise you against installing any sort of FXS or FXO card on the mainboard. Even if you do, the case is too small to allow most PCI cards to fit in. The Web interface is rudimentary, but adequate for run-of-the-mill commands (reload setting, restart asterisk, reboot machine, backup config files, and edit files).
What I like about the setup:
I bought the Soekris net4801 SBC from ebay (used) for about $115, incl. s&h. Purchasing the case from Soekris Engineering cost another $30. The 512 MB USB stick cost $10 from buy.com, and the 64MB CF card came free with the SBC. You can’t beat the cost and the bang for the buck!
I have had the setup for the past 2 months, and it hasn’t crashed once. Voice quality is flawless. The SBC is tiny (slightly larger than a CD case) and is passively cooled, and thus completely noiseless. The CPU doesn’t even have a heat sink on it! With the CF card installed, I estimate its power usage to be around 7-8 Watts. If you install a 2.5" HDD instead of the CF card, your power usage will go up - so avoid that if possible.
What is broken in the setup:
The voicemail-to-email feature is broken, but I think they are aware of the issue and working on it. I have had trouble getting the vm timestamps to work correctly for users in different timezones. (This is a by-product of using uClibc instead of glibc in the build). Finally, I haven’t been able to install the g729a license that I purchased from Digium, for transcoding g729a calls to gsm (for voicemail). I’m not sure if that’s due to a binary incompatibility or if it’s my stupidity.
On the whole, the setup seems to support 15-20 calls simultaneously as long as no transcoding is required. If transcoding is needed, then ymmv. But I think you can probably do no more than 3-4 calls simultaneously in that case. In any case, you will probably hit your upload bandwidth limit on your Internet service before you hit the SBC’s limit on simulateous calls.
Finally, I am also using a Linksys SPA-3102 as a VOIP-PSTN and PSTN-VOIP gateway. Works well, in general. However, the SPA seems to have echo issues with a Panasonic cordless phone connected to the FXS port, on PSTN calls. But as long as I use a proper IP phone (GXP-2000), the echo isn’t noticeable on PSTN calls.