Nepal earthquake: how do cell signals get through?

Kathmandu Valley, UnitingNepal

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Headlines about Nepal praise Google and Facebook for their "collaborative, cellphone-based tools [deployed] over the weekend to help track victims of the earthquake (Washington Post)." My question is--how do the signals get through? The country has experienced an earthquake of magnitude of 7.8 to 8.1 (Wikipedia), so power stations, cell towers, and network infrastructure must have been badly damaged.

Reuters in one of their reports published this map:

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Nepal,earthquake map, Reuters

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Currently, there are 6 colocation data centers in Nepal, all of them are located in Kathmandu. This suggests that the cellphone signals are being processed by sites situated elsewhere or by other means.

It looks like Nepal is a magnet for adventurers wanting to trek in the Himalayas. The Mountain Company's FAQ, answering the question "Do mobile/ cell phones work while on trek?," says:

Over the last few years the mobile/ cell phone network has improved significantly in more remote areas of Nepal. There are now cell phone masts installed at Gorakshep so it is possible to get 3G connectivity throughout the entire Everest Base Camp trek.
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In more remote regions of Nepal such as on Dhaulagiri Circuit, Manaslu Circuit and Tsum Valley, Kanchenjunga Circuit, Upper Dolpo treks there will be no mobile/ cell phone coverage. On these trips we send a satellite phone with our groups for communications and our clients are welcome to use for personal calls and SMS texts if they like. 

Also Indian telecom companies are lending a hand.

Indian telecom companies have made calls to Nepal discounted or completely free. Messaging app Viber has made outgoing calls to landlines and mobiles free users of its Viber Out service.

The 2 companies most mentioned in information about cell service in the Nepal area are Nepal Telecom and N Cell (Facebook link, website unavailable).

This is what I could find; I hope you find it useful.

-- Marge