Analyst Maynard Um noted that the new total is up from 316 partners in mid-April, and 280 carriers last October. That means Apple has increased its carrier count by 15.4 percent over the last 7 months.
According to Um, Apple's partnerships in the wireless industry were fairly stable in 2011 and 2012. Since then, Apple has become aggressive in adding more carriers --?a move that likely helped boost surprisingly strong international iPhone sales last quarter.
"Assuming these carriers also get the new iPhone at launch, this could help year over year unit sell-in numbers," Um wrote.
The analyst also increased his "valuation" range for shares of AAPL stock from $595 to $640. Compared to his colleagues, Um has been bearish on Apple in recent months, and his previous valuation range topped out at $585, even while shares of AAPL had been trading at well over $600 for weeks.
In fact, as of premarket trading on Friday, Apple was already at nearly $640 per share, putting it in a position to break out of Um's valuation range on the same day he adjusted it.
Um admitted on Friday that he doesn't see many negative catalysts for Apple through the fall, as the company is expected to introduce new product cycles. But he also said he believes "material upside could be limited," particularly beyond calendar 2014.
The analyst has maintained his "market perform" rating on AAPL stock, and continues to believe that Apple will eventually have to choose between average selling price and margins versus unit sales and market share.