Help for a dialplan

how to realize call transfer from one extension to another extension?
the following is the detail request:
softphone A have a id such as 88205384
and softphone B have a id such as 88204578
A call B use 88204578 but A donot want to contact with B directly. when B accept the phone the phone transfer to another extension such as a special extension 1000
the 1000 dialplan like this:
[context]
exten=>1000,1,mp3player(…/a.mp3)

such a reqirement can be realize or not ?

any hints will be great appreciated!
thanks very much!

Yes, it is possible to do call transfers with Asterisk. Some of the features may be seen here:

voip-info.org/wiki-Asterisk+PBX+functions

How you transfer depends more on the endpoints. For example, the X-Lite softphone from CounterPath handles the transfer as a set of SIP messages. While with a Sipura ATA and an analog phone you may do a ‘flash-hook’ method of attended transfers.