This is just a gimmick by different airlines to get more business. They do not allow transfer of airmiles from one airline to another. Not only that, they do not allow to transfer airmiles even from different members of families.. We should just forget about these airmiles and fly on the airlines with the cheapest airfare and better service.

It would only be via an agreement between airlines. I have a lot of airmiles with one airline which must be exclusively used with them - if not with flights then with their online shop for luxury goods.

It can be done only if the airlines are having some alliance....

First off, the airlines you wish to transfer to must be a part of a same alliance. Like- I can transfer NORTHWEST AIRLINES miles on KLM ROYAL DUTCH & vice versa. But you can't transfer say- Air India miles to say- Pakistani International AIrlines miles.

Although you can't swap miles directly between airline accounts, you can take advantage of middleman sites to transfer useless miles into your preferred loyalty program, where they can help you reach an award level.

Airline credit card provides you miles. There are ways of converting miles from one airline to another, but not just transferring them directly, like you might move money from savings to checking. There is an exchange rate, and not all miles will transfer in the conversion. You can use calculator and planner at Webflyer.com that offers conversion alternatives. You can also exchange miles within any airlines using systems like points.com but it has some penalty/charge.

Source: http://www.creditcardassist.com