Missing: 77 million mobile phones

Gartner’s and IDC’s sales estimates don’t always agree, but this is absurd.

Much was made Wednesday in Gartner’s latest Worldwide Mobile Phone Sales report, and in subsequent news coverage, of the sudden surge in the sales of so-called “white box” mobile phones in the third quarter of 2010.

According to Gartner, these unbranded phones are being snapped up in such huge numbers in Asia and elsewhere that the major manufacturers have started to give ground to the “Other” category, which by Gartner’s count more than doubled year over year and now accounts for 33% of all mobile phone sales, more than Nokia (NOK), Apple (AAPL) and HTC combined.

All of which struck Asymco‘s Horace Dediu as odd. “Doubling share in a year is possible if you’re at 1% share,” he writes in a note posted Thursday morning. “But to double from a base of 16% is sounding improbable.”

To check Gartner’s claims he compares its Q3 sales report to IDC‘s, issued two weeks earlier. What he discovered was that in the same three months, IDC counted sales of 340.5 million phones and Gartner counted 417 million — a 77 million unit discrepancy that is more than enough to account for the unusual growth in Gartner’s “Other” category.

“If Gartner is right,” Dediu writes, “how could IDC miss 77 million phones? If IDC is right how did Gartner conjure up 77 million phones in one quarter? That number is nearly as big as all the smartphones sold (81 million). This is not within any margin of error for whatever sampling method they use. Perhaps they need to clarify this because until they do, neither is credible.”

We’ve put in requests to both Gartner and IDC.

HIGHLY RECOMMENDED: The comment posted at 11:29 from a former IDC analyst who tells us more than we may want to know about what he calls “this sausage-making process.”

Meanwhile, we note that the two companies do use different methodologies. Garner counts sales to end users (“sell through”) and IDC counts sales into channel (“sell in”). But in normal circumstances, one would expect the IDC’s sell-in number to be larger than Gartner’s sell-through, not the other way around.

My Gartner PR contact writes:

I’ve spoken with the analysts, and the difference in numbers is very likely down to the white box market. There’s commentary in yesterday’s release.

Effectively, many companies can now assemble large numbers of handsets cheaply using readily-available components — in much the same way that white box PC manufacturers were able to do so in the past. These companies are increasingly exporting to countries with high demand for basic handsets. Combine that with differences already noted in how mobile device sales are measured, and you get to the root of things.

Another bit of research that might be relevant:

Gartner Says Indian Mobile Handset Sales To Reach 138.6 million in 2010