T-Mobile Kids Are Free promo offers three free lines until 2012

Has your kid been begging you for a cell phone? If so, take note: T-Mobile is offering up to three free lines to new and existing customers with a qualifying family plan. As part of the Kids Are Free promotion, there is no monthly charge for up to three additional lines until January of 2012, a savings of $5 a month per line or close to $100 per line for the full length of the free period.

With a recent survey by PEW Internet Research finding that 75% of teens already have a cell phone the promotion is a good deal for parents who want to switch service or are looking for a way to stop the nightly complaints of, "Everyone else has a cell phone. Why can't I?!?"

T-Mobile family plans that qualify for up to 3 free lines start at $59.99 and don't include texting, but if you're equipping three teens with cell phones you can invest in a $20 a month upgrade to outfit all of your phones with unlimited texting. If mobile web is in the plans you can also add those options to the family plan or to individual lines. T-Mobile is offering a Buy One Get One free after rebate deal on the Samsung Vibrant and savings on all messaging phones as part of the promotion.

The Kids Are Free promo runs Sept. 8 through Nov. 2 and can be used with a two-year contract for a discount on your new phones or without a contract, but a higher up-front cost on the phone. In this case, since you are getting the service free for close to a year, and at $5 a month after that you may be better off taking a deep discount on your phone up front and signing a contract, but you'll need to weigh those options yourself.

Before you sign up be sure to check out the Ultimate Cellphone Plan Comparison chart that looks at all the costs across carriers and pricing levels as well as checking out BillShrink's Cell Phone Advisor tool that can help you analyze your current usage and find the best deal at the best carrier.