There’s been much debate over whether Apple will release its iPhone 5 in September or October, but Forbes’ Brian Caulfield writes in an article from last Monday, an October release would seriously affect the company’s third-quarter numbers.

“That could cut the number of iPhones sold during the quarter ending in September by 2 million units to 20 million from 22.0 million units,” reports Caulfield, citing a recent research note by Piper Jaffray analyst Gene Munster.

As Munster says, there’s plenty of demand for a new iPhone, and those phones not sold in 2011’s third quarter, which runs from July through September, would be sold in the final quarter, which will continue from October until the end of the year.

“We recently surveyed a small sample of 216mobile phone users about their phones and carriers. Survey results were positive for Apple’s iPhone,” reports Munster. “Among our respondents the iPhone’s market share could more than double throughout the next round of phone purchases. Our survey also shows significant pent up demand for the next iPhone, particularly at Verizon. Among VZ subscribers that do not already have an iPhone, 55% expect their next phone to be an iPhone; the majority of those (74%) are specifically waiting for the iPhone 5.”