Today’s iPhone 5 rumor bypasses the “if” it’s going to launch on Sprint question and jumps right ahead to specifics of that launch.

According to sources “familiar with the matter” as quoted in Bloomberg, the iPhone 5 will most definitely be arriving on Sprint. And when it does, it will come with an unlimited data plan.

This move would make Sprint the only wireless carrier to offer the iPhone with an unlimited, flat-rate data plan. Carriers like AT&T used to offer the unlimited plan, but have since moved to a tiered data structure.

The sources also confirmed the mid-October release date, the most widely accepted rumor nowadays regarding the upcoming device. To prepare for the iPhone 5 launch, they said, Sprint has postponed the debut of a rival 4G phone that was supposed to launch this month.

It’s pretty easy to understand why Sprint would take this step. They are in 3rd place among wireless carriers, a good deal behind AT&T and Verizon. This kind of offering could make a splash right when the iPhone 5 drops, but could it really draw a significant amount of customers away from the big two?

CNET quotes an analyst who thinks the unlimited offering, if accurately predicted, would only last for a brief time.

“There’s a good chance they will use this to pull subscribers from AT&T and Verizon,” said Maribel Lopez, an analyst at Lopez Research. “After a certain time, they won’t offer the unlimited option any more.”

It remains to be seen if that would actually be an effective strategy.

Here’s everything we know about the iPhone 5 coming to Sprint:

• Early reports indicate that the phone will launch sometime in mid-October.  That source named an actual date – October 7th.
• Late last month, an internal memo leaked that showed Sprint upper management directing employees to keep mum regarding the iPhone 5 release.  They were specifically instructed to give a “no comment” response when any customer asked them directly.
• Earlier this week, a Best Buy document surfaced detailing a probable early October release date for the iPhone 5 as well as a release on Sprint.
• Last, we heard that Sprint was installing network repeaters in Apple stores in order to boost signal quality for next month’s release.