I just had a word with representative from AT&T....There is no way you can used any smartphone without data plan...If you put your SIM Card  in any other smartphones you will automatically  see the data plan charge on your bill you do not even have to make any calls....That is what it happened on my last month bill...so better get the $15 data plan which gives you 200mb Data plan use for a month...as you said you have wifi on ur office and work that should be more then enough.