asterisk users - Sep 2013 - OpenVox G400P network registration problems

Is anybody intimately familiar with the OpenVox G400P card, or the Quectel M20 
RF modules fitted to it?  

I am having a strange network connectivity issue with just such a card, as 
follows:

The card was previously used with four O2 SIMs, and -- once I mastered 
creating message PDUs! -- worked beautifully, save for the fact that O2's 
definition of "unlimited" as in text messages turned out not to be the
same as
that found in the Oxford English Dictionary :(

Replacement SIM cards were duly ordered, and this is when the problem has 
manifested itself.

Span 1 will not register a T-Mobile SIM. Issuing AT+COPS=? shows only O2 and 
Vodafone available as operators on this span. Issuing the same command on any 
other span shows Orange, T-Mobile, O2 and Vodafone available. The SIM however 
worked properly in a mobile phone handset.  Performing "gsm power off
1", "gsm
power off 2", swapping the SIMs between these spans and then performing
"gsm
power on 1" and "gsm power on 2" results in the recalcitrant SIM
registering
on span 2, and the SIM formerly from span 2 not registering on span 1.

I'm guessing the Quectel M20 GSM module on span 1 has got itself into a 
strange state; because it was also necessary to issue "gsm show span
1" to
read the result of the last AT command (on other spans, the result appears in 
the Asterisk CLI). Do you know of a way of hard-resetting it? (The obvious 
"ATZ" does not work, neither does "gsm power off 1" followed
by "gsm power on
1").

Software versions:
Debian GNU/Linux 6.0.6
Asterisk 1.8.11-cert5
Dahdi 2.6.1+2.6.1
Chan_extra 2.0.5
(Yes, these are all a bit out-of-date; but they worked before.  All I did was 
swap over the SIM cards.)

-- 
AJS

Answers come *after* questions.

It took an OpenVox engineer to sort out this obscure problem in the end, but 
it was pretty much as I suspected:  the Quectel M20 GSM module serving span 1 
was stuck in an unusual state, in which it would only operate in the 900 MHz 
band.  Fine for O2, Vodafone and Tesco; but no good for T-Mobile or Orange!

What fixed it was this:

cli> gsm send at 1 AT+QBAND=\"GSM850_EGSM_DCS_PCS_MODE\"

(note the backslashes before the speech marks).

I had actually *almost* managed to work this out for myself, except for 
missing the backslashes; without which, it didn't work.


Anyway.  If you have a G400P card  (or, presumably, a G400E -- which uses the 
same GSM modules, just has a different host interface)  and some SIM slots seem 
to be locked to a particular phone company  (or group of phone companies)  
then this might well be what is up with yours.

Check with

cli> gsm send at 1 AT+QBAND@

(Replace 1 with the number of the misbehaving span.  The CLI will replace the 
@ sign with a question mark.)   If the response you get is anything other than

+QBAND: "GSM850_EGSM_DCS_PCS_MODE"

then this fix is what you need to do.  (If you get no response at all, then try

cli> gsm show span 1

which will include the result from the last AT command -- assuming it hasn't
been overwritten by a signal strength report in the meantime, in which case 
repeat the AT+QBAND@ command.)

-- 
AJS

Answers come *after* questions.