Hiya,
I've been doing some testing with SMS in Belgium (Belgacom), sending SMS 
seems to work fine. (with .call file and a context that handles the sending)
The problem is however, receiving.. Hardware and software is quadBRI 
from Junghanns, bristuff RC8h (asterisk 1.0.8), Debian 3.1.
For receiving SMS in asterisk, I am using:
[custom-smsrx]
exten => s/0171701,1,Verbose(Receiving SMS from ${CALLERIDNUM})
exten => s/0171701,2,Answer
exten => s/0171701,3,Wait(1)
exten => s/0171701,4,SMS(from-pstn,a)
exten => s/0171701,5,Hangup
I do get some logging that shows me it seems to work, but nothing gets 
written to the /var/spool/asterisk/sms dir.. Here's the log:
Jul 14 15:17:30 VERBOSE[12055]:     -- Executing Goto("Zap/5-1", 
"custom-smsrx|s/0171701|1") in new stack
Jul 14 15:17:30 VERBOSE[12055]:     -- Goto (custom-smsrx,s/0171701,1)
Jul 14 15:17:30 VERBOSE[12055]:     -- Executing Verbose("Zap/5-1", 
"Receiving SMS from 0171701") in new stack
Jul 14 15:17:30 VERBOSE[12055]:     -- Executing Answer("Zap/5-1",
"")
in new stack
Jul 14 15:17:30 WARNING[12055]: Unable to request echo training on channel 5
Jul 14 15:17:30 VERBOSE[12055]:     -- Executing Wait("Zap/5-1",
"1") in
new stack
Jul 14 15:17:31 DEBUG[12055]: Scheduling timer at 160 sample intervals
Jul 14 15:17:31 DEBUG[12055]: Generator got voice, switching to phase 
locked mode
Jul 14 15:17:31 DEBUG[12055]: Scheduling timer at 0 sample intervals
Jul 14 15:17:33 VERBOSE[12055]:     -- SMS RX 91 8D 00 0A 81 20...
Jul 14 15:17:33 VERBOSE[12055]:     -- SMS TX 95 02 00 00 69 00...
Jul 14 15:17:35 VERBOSE[12055]:     -- SMS RX 91 8D 04 0A 81 20...
Jul 14 15:17:35 VERBOSE[12055]:     -- SMS TX 95 02 00 00 69 00...
Jul 14 15:17:36 VERBOSE[12055]:     -- SMS RX 94 00 6C 0A 81 20...
Jul 14 15:17:36 VERBOSE[12055]:     -- Executing Hangup("Zap/5-1",
"")
in new stack
Any idea.. anyone?
Cheers!