Need advice about the O2 price increases and Virgin Volt deal

My wife has an O2 SIM-only pay-monthly deal [it's not a contract], for which she is currently paying £11.50 [which will be going up by £2.50 next April to £14] a month, but it gives us the Volt deals with Virgin.

So could I cancel my wife's monthly deal in January and then when my current Virgin Volt deal ends in February can I then go with Virgin for everything,i.e. the mega volt package which includes an O2 sim deal which would then save me the £11.50 [going up to £14 a month in April]my wife is paying for her current month-to-month Sim Only deal?

If you think what I'm saying is correct, does my wife have to give ex-amount of time to cancel her current month-to-month O2 SIM-only deal?

Sorry if that's a tad complicated, but I can't think of a better way to put my dilemma into words