If you think it’s just AT&T’s network in the United States that’s being overwhelmed by the iPhone, think again.

According to AppleInsider (from a Reuters report), U.K.-based carrier O2 has also been battling data network congestion on the other side of the pond for the last six months or so. O2 has seen an 18-fold increase in traffic from data-gobbling smartphones -- so much so that O2’s London network reportedly crashed under the pressure on numerous occasions this past summer. During those outages, many customers were unable to make calls or get a data connection at certain times.

“Where we haven’t met our own high standards then there’s no question, we apologize to customers for that fact,” Chief Executive Ronan Dunne confessed to the Financial Times. “But it would be wrong to say O2 has failed its customers en masse.”

It would seem that O2 has been working hard to correct the situation, including a $48 million investment in its network in & around London which included 200 extra mobile towers. Most of the network strain appears to have eased by year’s end with the upgrade.

Hopping across the Pacific pond, it appears the iPhone is finally gaining some traction in China after the widely reported lackluster launch, lack of Wi-Fi and competition with the grey market.

China Unicom, Apple’s exclusive carrier in that country, is now believed to have sold its 300,000th device earlier this week. Less than three weeks ago, the carrier had hit 100,000 units after 40 days, so the new report could be more good news for Apple to cap off 2009.