Just some guesses or ideas… (I’m neither an expert in cellular radio technology nor do I own such a Gadgeteer module, so just take it as a starting point for further research!)
It seems that the cellular radio module basically does AT commands.
MMS needs to be transferred by an internet connection with an MMS gateway, data format is somehow similar to email. I suppose that you’ll not be able to connect to such a gateway anyway, because their data (connection details, protocol, etc.) might not be publically available.
Possibile alternatives:
Use SMS. Does not support non-text data, but helpful for near-immediate notification.
Use Internet via GPRS: You can then send any data to any server:
Email via SMTP should be possible. Use HTTP to send data to a messaging gateway, that can forward push messages to iOS or Android devices. You can even get an account for a web-based messaging gateway to send SMS or MMS via HTTP.
Maybe this is some helpful information to extend your research… If I’m plain wrong and anybody knows how to support MMS anyway: I’d be interested to know, too.
I have not done this myself, but have lots of experience of using embedded systems and modems to send and receive data so I did a little quick search on the topic.
To be able to do MMS you will need 2 things.
GPRS connection using the MMS gateway APN from your network. If you check your handphone you will see that it has 2 GPRS settings, 1 for data and the other for MMS. You can also check the MMS settings to get an idea of the values you need.
The MMS protocol. This is basically a TCP/IP connection so you will need to have a PPP connection to your modem or the ability within the modem to do a TCP/IP connection if your .NETMF does not support PPP over GPRS.
Some useful info on this Wiki page which refers to some details and specifications you need.
I checked some gateways, and it seems to be possible to send an mms with a connection to a server with HTTP GET/POST.
It looks like most parameters are pretty simple, but one of them is the picture in a SMIL document, which is a link to the picture, residing somewhere else.