welcome to the family~

Untick mobile networks at settings -> wifi and networks -> mobile networks....
You have to go settings -> wifi and networks -> Mobile Networks  and tick it.... then only you can use... but before that, check if there is anything (apps or widgets) you set to auto refresh because it WILL cost you your data..

as for both of you i suggest create a shortcut on the home screen for tuning mobile network on or off when you need it... unless you signed an unlimited data plan....

you can always disable auto updates/refreshes for most of the apps and widgets of social networks...

I dont know about others but im using Digi... not using 0.facebook.com but instead im using touch.faebook.com (yes this takes data costs),
I dont load videos, i just merely check on updates of my group/event in facebook, whilst the auto refresh of news feed goes...
I disabled auto refresh for tweet deck home tab(all updates) but enabled auto refresh at Me tab(only updates about me)...
I Foursquare at new places..
I sometimes even browse websites with mobile network....

after all these i still dont use much data plan.. not to mention digi gives free data after reloading.. so basically 10Mb is enough to use for more than 2 weeks for me...
as long as you dont load videos or download or heavy usage of data plans, you wont lose much...

of course i turn off mobile networks when not used.. since i did not sign for a unlimited data plan...

you should spend some time and money to find out if what you are using, your mobile network, is really that costly because i find it not THAT fast... unless you start refreshing things ALOT and browse alot....

Hie ,
Can recomend  apps to  d/load the change the  fonts on the  phone  ? 

Thank you