Stop it! Don't start off by deciving. I suggest you just keep the line, and the CHEAPEST plan they have with no data, text, etc.
You never know when you'd have to switch back to that line because something happens at work...
I have the same situation. At work I have an AT&T line/account, and with T-Mobile I have a personal account. I've since suspended my T-Mobile account ( a feature T-Mobile offer for long time customers), and thus pay $10 a month (ETF is $200). That way if anything happens, I still have my personal line