Earn 25,000 miles on United, Northwest or Delta for each phone and service agreement you purchase from Nextel through March 31st — up to 125,000 miles.

Alternatively, you can earn 16 Southwest Rapid Rewards credits per phone and plan, up to 80 credits.

Most purchases require a two-year service agreement and carry a $200 early termination fee.

Read the fine print on the offer you’re considering, though.

First, the miles won’t all be posted right away. Instead,

Miles will be awarded as 2,000 miles after 30-days, 1,000 miles per month for the next 21 months and 2,000 miles after the 23rd month.

Second, the Delta and Northwest offers for 25,000 miles per phone are only available to elite members — at least that’s what the terms and conditions say.

The Southwest offer says it’s valid only for recipients of the Nextel email offer.

The United offer doesn’t contain any of those requirements at all, so that’s the one I’d go for — and I’d print out and copy of those terms and conditions and save them.

Update: There’s a Notiflyer up about this offer.