OK, I finally managed to get MMS working, however... well, read on.
Configuring your handset to use MMS is not easy. That's why B-Mobile has this system in place where you send them information about your phone make and model, and they can help you configure the phone. This is usually done by a special configuration message sent to the phone, so the user does not need to bother entering the information manually. However, my phone is not a standard MMS-capable phone, so I guess B-Mobile couldn't configure it remotely. I waited in vain. And for some obscure reason, B-Mobile does not advertise their MMS technical information on their website. (TashiCell's MMS configuration information is available on their website).
Eventually I got hold of the required information. Here it is. If your phone supports MMS, there's usually some menu where you can put in this information. Caution - use it only if you know what you're doing:
Access Point Name: mmsbt
Username: (leave blank)
Password: (leave blank)
Gateway/Proxy address: 192.168.20.10
Gateway/Proxy port: 8799
I entered this set of cryptic numbers and characters into my phone and - voilà! - I can now use MMS to send photos, audio etc to other phones. So some progress is made! Hooray!!!
However - and there always seem to be an "however" - some stuff still doesn't work. Sending an MMS to an email address seems to be broken. After sending an MMS to an email address, I get a "message delivered" response, but the MMS never reaches the email recipient. I've notified B-Mobile about the glitch. Let's see what happens.
To be continued!