The iPhone 6S wars have started and two retailers have fired the opening shots with crazy but sweet deals that should get customers trooping to their respective stores soon.

T-Mobile was the first to fire the opening salvo, initially offering the iPhone 6S at $20 a month. Thereafter, Sprint announced its own package, a lower $15 per month for the same handset.

Not to be outdone, T-Mobile counters with a sweet option involving trade-ins of an iPhone 6. For folks who trade in their iPhone 6, they can get the latest iPhone 6S at $5 per month. Additionally, for folks who are still using the iPhone 5S, you can also avail of the deal only that you will be paying a slightly higher fee of $10 per month.

The offer is also valid for folks who may have pre-ordered the iPhone 6S. Aside from that, the deal also includes T-Mobile's Lifetime Coverage Guarantee and a full refund in case folks decide to return the iPhone 6S within 30 days of purchase. If returned over the 30-day period, folks get a one-month reimbursement and the device will be unlocked for use with another cellular network.

Over at Sprint, the retailer offers its own deal, which would see customers get a new 16 GB iPhone 6S for $1 a month or an iPhone 6S Plus for $5 monthly if they trade in their old iPhone 6. The deal is for a limited time only.

For the ones who may be interested in the deal from Sprint, take note that prices may vary depending on the type of iPhone 6S/6S Plus model that would be purchased as well as the quality of the iPhone 6 being traded in.

In this case, customers could end up paying $5.77/month (64 GB) or $10.53 (128GB) when purchasing an iPhone 6s, and $9.77/month (64GB) or $14.53 (128GB) when buying an iPhone 6s Plus. Another thing that should be placed in consideration is that monthly subscription charges could vary as well.