As Xinhua said the phone conversation was initiated at Biden's request, it is impossible to think that the men did not discuss Wang's case, given the timing. Indeed, on the same day, Wang reportedly "left of his own volition" and was taken by national security agents to Beijing, resulting in one of the biggest political crises in recent decades and the downfall of Chongqing party boss Bo Xilai , who was then one of the mainland's rising political stars.

Fast forward to today. Since US whistle-blower Edward Snowden broke cover and announced his presence in Hong Kong last week, Beijing again has remained silent. The foreign ministry spokesperson refused to comment on Snowden's case directly and chose to broadly urge for deeper co-operation over cyber security between the two countries.

Although mightily pleased inwardly, mainland officials were wise to bite their tongues. The explosive revelations by the former NSA contractor about top-secret US surveillance of the global internet was the best evidence of Washington's hypocrisy at a time of its increasing public denunciation of China's state-sponsored cyber hacking operations.

Again, the timing was very sensitive. Snowden's astonishing disclosures came days after the presidents of China and US held seven hours of informal meetings to cultivate stronger ties based on mutual trust - characterised by Xi as "a new model of major power relationships".

In an exclusive interview with the Snowden said he would seek refuge in Hong Kong, and placed his faith in the city's people and its rule of law. But the fact remains that his fate is most likely to be decided by Beijing and Washington. By coincidence, the Snowden case fell into Xi's lap as a birthday present as Saturday marked the president's 60th birthday, an important anniversary to celebrate in the Chinese calendar. No doubt, how to resolve it would again test his wisdom and that of the entire Beijing leadership in the context of Sino-US ties.

While Xinhua has carried no reports of a phone conversation from Obama congratulating Xi on his birthday, it is interesting to note that Russian President Vladimir Putin called on Saturday to "discuss bilateral ties and the situation on Korean peninsula". The conversation contained nothing newsworthy, just the usual diplomatic language. But the one sentence quoting Xi as saying that he cherished his personal friendship and mutual trust with Putin seems to suggest that the Russian president called to congratulate the president on his birthday. In another interesting development, on the same day North Korean leader Kim Jung-un sent a birthday message to Xi, calling for stronger ties, according to the North Korean state media. Strangely, however, Chinese state media made no mention of Kim's message. It was quite uncharacteristic and could suggest an open snub against Kim amid North Korea's recent reckless behaviour.

Did Putin and Xi talked about Snowden's case? Your guess is as good as mine but the phone call came days after the Kremlin reportedly offered refuge to Snowden.

As one top foreign policy adviser to the Chinese leadership told the last week, Beijing would handle the Snowden case discreetly and had no interest in turning the event into a political case. If that reflects Beijing's thinking, the options of allowing Snowden to be extradited to the US or seeing him seek possible asylum in Hong Kong are not ideal as both would involve a lengthy court process and could strain Sino-US ties and create further complications for Hong Kong's political situation.

That leaves the third option that China would provide necessary assistance for Snowden to go to a third country. Under the circumstances, that would be the optimal solution.