Two reports published Thursday — one by IHS iSuppli, the other by Strategy Analytics — describe the global race for smartphone supremacy as high-stakes see-saw.

Basically what happened is that Apple (AAPL) took the lead from Nokia (NOK) in June, lost it to Samsung in September and won it back in December.

“Apple’s introduction of the 4S in the fourth quarter unleashed tremendous pent-up demand for the iPhone as consumers awaited the arrival of the latest model,” said IHS senior analyst Wayne Lam. “This caused the company’s smartphone shipments to surge, allowing it to retake market leadership by a slight margin. However, Apple and Samsung continue to run neck and neck in global smartphone shipments, setting up a tight battle for leadership that will continue throughout 2012.”

Although the two firms are tracking the same markets and using the same metric (shipments, rather than sales to end users), their numbers differ by as much as 2.5 million units. IHS has Samsung shipping 95 million smartphones worldwide in 2011 (see spreadsheet above). According to Strategy Analytics, the Korean company shipped 97.4 million.

But they both agree that Apple, which reports its sales with considerably more transparency than Samsung, sold 93 million iPhones in 2011.

Below: The Strategy Analytics spreadsheets.