Even as Sprint (NYSE:S) waits for federal regulators to consider its merger with T-Mobile (NASDAQ:TMUS), it still has to focus on its own operations. Moving forward, it's going to continue to employ some of the strategies it currently uses to gain customers -- but amp them up.

The No. 4 wireless carrier has added customers in the past by using extreme discounting -- Sprint knows it's at a disadvantage when it comes to customer perception, so it has used lower prices to entice people to sign up. That's worked to a point: Low prices have led Sprint to three straight years of net postpaid additions. Now the company is doubling down on that strategy by undercutting its rivals dramatically with a new $15 per month offer for unlimited data, text, and calls. It's a bold deal, and one that should win the company customers, but it's not for everyone.

T-Mobile CEO John Legere (left) and Sprint Executive Chairman Marcelo Claure

T-Mobile CEO John Legere (left) and Sprint Executive Chairman Marcelo Claure are seen at the press conference to announce their companies' merger. Image source: Getty Images.

How does the $15 Sprint deal work?

Sprint's offer is legit, but it does have some caveats. The biggest issue is that anyone electing to take the deal must either bring a phone that works on the Sprint network or purchase one outright. The carrier won't be offering the option to lease or finance a phone to anyone who elects to take the $15 deal.

In addition, anyone opting for the cheap plan won't be able to use their phone as a mobile hotspot. They will also only get standard-definition video -- not the high definition video offered in its traditional unlimited plan. Gaming and music will also be offered at slower data rates.

Still, if you have a phone or are willing to purchase one, Sprint is offering significant savings. Its regular Unlimited Freedom plan charges $60 for one line and $100 for two. With the $15 "Unlimited Kickstart" plan consumers pay $15 for each line they purchase.

Sprint will only offer the $15 deal through Friday, June 15. It has not said how long it will honor the pricing for customers who sign up. All pricing requires customers to set up auto-pay, and all Sprint unlimited plans are subject to throttling during heavy traffic periods.

Is this deal worth it?

If you own a phone (or will buy one) and can live without using your device as a hub, the pricing makes this offer very appealing. T-Mobile, which is usually the lowest-priced carrier after Sprint, charges $70 for one line with unlimited everything. That price goes down to $40 per line when a customer gets four lines.

You can get four unlimited Sprint lines for less than the price of one from T-Mobile. It's hard to argue with that deal, even if joining Sprint means accepting a slightly inferior network -- assuming you live somewhere with decent Sprint coverage.