By Katie Marsal

Published: 03:05 PM EST (12:05 PM PST)

With Apple having announced iPhone shipments far in excess of reported activations, the ongoing debate about exactly what happened to all those other "missing" units continued on Friday, with investment bank Piper Jaffray weighing in with its own explanation.

According to the firm, Apple sold 3.7 million iPhones during the three-month period ending December, 2 million of which were confirmed by AT&T to have been activated on its US wireless network during that same time.

Taking a closer look at the remaining/missing 1.7 million units, analyst Gene Munster said in a research note that believes another 350,000 were sold throughout Europe during the same time period and another 838,00 were sold with the intent that they'd be unlocked.

Munster arrived at the latter figure by using Apple's own estimation from back in October than approximately 22 percent of US iPhone sales were being purchased with the intent that they'd later be unlocked from AT&T's network. The analyst, however, rounded that estimation up to 25 percent of the 3.7 million units given that unlocking has since "become easier."

That still leaves 512,000 iPhones which are unaccounted for, but Munster maintains that these units are likely spread across the company's US and European distribution channels and that the level of inventory is "consistent with Mac and iPod levels over the past 3 years."

Specifically, he believes 220,000 units are spread between Apple and AT&T outlets in the US, with the other 292,000 peppered around authorized resellers in the UK, France and Germany.



While slightly less than the 670,000 in channel inventory estimated earlier this week by Bernstein analyst Toni Sacconaghi, Munster's figure is well within the same ballpark.

The end result: there are likely only several hundred thousand units unaccounted for -- rather than nearly 1.5 million -- because they comprise Apple's normal level of channel inventory, estimated by Munster to be approximately 5 weeks in the case of iPhone.