Well, without [Wireless & networks/Mobile networks/Data enabled]
checked you will will not be able to send MMS: plain and simple. You want to send a picture over your 2G phone carrier: yes there will be fees for that.
You don't want any other things to use 2G data while you send your MMS: fair enough! So now you have to learn how to do that.
So you could spend some time going through each and every application and service on your phone that might do so and disable any automatic updating: for emails, facebook, Market ads and what not... but it could be tedious.
The easiest way for you to achieve this would be to use Droidwall [like I originally referrred to above

]. In there you will find 2 modes: 1- black list that blocks selected apks to access either wifi or 3G/data and 2- white list that does the opposite.
So install Droidwall [free from Market], make sure you select
black list mode on top. And oh! you need root to use this so make sure that you also click "Allow" and check the 'remember' box when you see the Superuser permission request screen the first time.
Once that is done, seleck/check everything on the second column EXCEPT "
Messaging"
AND the first box called
"(Any application)- Same as selecting all applications"
Additionally, select any application from the first column that you KNOW should not access internet at all (on wifi this time) --> as a bonus, doing so will block any ads from those free applications
Press the menu button and press "
Apply rules" [or "save rules" the first time??] and make sure that you see "
Firewall enabled" with a green line through it.
On the picture attached, you can see that I've selected the (Any application) for 3G/data instead of all except the 2 I told you. I leave it that way to block all data and when I need to send MMS, I unchecked it (and press "apply rules") for just the short time of sending the message then I re-enable it afterwards.
Any other questions? Lol - just joking I'm no Android help line hehe!
But I hope that this helped you guys; if so, you can log-in and hit that "Thanks" button here bellow: -->
Cheers