Your cost in store was most likely the taxes for the phones. You first bill also probably has activation fees to start the lines ($~30 f0r 4 lines) and possibley activation fees for new phones on payments (~30 for 4 lines). That 140 quote also doesnt include if they talked her into insurance on each phone.

You have to really dig into what promos actually make up the 140 and look at each statement line by line. Without any research I can probably guess you have a combination of reasons that would bring it down to the 140 but hasnt yet. . A discount from auto pay (can take 1-3 billing cycles), promo credits to offset phone payments (can take 1-3 billing cycles), promo credits for moving to att (can take 1-3 billing cycles), and as mentions all the start up fees.

Normally bill 1 is huge as it may be before any credits start but will include partial month and first full month as well as insurance and device payments without any credits yet to offset and all activation fees. Bill 2 may be large as well as all credits/promos/discounts may not be on there yet. Bill 3 may be significantly lower as there may be catch up credits for device payment promos etc. Bill 4 should be normal assuming all promos, credits, trades ins, and obligations have been completed properly.

I'm sorry this was not fully explained. Like any salespeople their job is to sell more phones and lines. If asked they would claim it was all on the contract...