It means switching from one provider to the other - a common feature in the mobile phone sector.

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Note added at 5 mins (2005-06-21 07:04:22 GMT)
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2 Churning

Churn means the discontinuation of a contract with a business [Brown 00]. In many European countries market structures of wireless telecommunications have changed in the last years form monopolistic to very competitive markets [Edmonds 97]. To be able to control and reduce the customer churn rate may be a vital factor for the survival of mobile phone companies [Edmonds97]. In particular it would be necessary to prevent the churning of profitable customers. If it is possible to predict whether a customer is likely to churn in two months, given today’s customers record, appropriate action on the side of the business may prevent the loss of the customer. In order to prevent the churning of customers, however, it is necessary to know WHO the churners are. Furthermore it is important to know WHY a customer decides to discontinue a contract.

http://66.102.9.104/search?q=cache:9r8-0EEINB0J:www.mathemat...

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Note added at 17 mins (2005-06-21 07:16:03 GMT)
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Churn rates — the proportion of subscribers who switch from one operator to another each month — soared. In three years, 5m subscribers switched operators and kept their numbers, in a territory with a population of 7m. The lesson for America\'s hyper-competitive mobile industry, it seemed, was clear: portability would be great for users but terrible for operators.

http://www.economist.com/displaystory.cfm?story_id=2249318