According to Wikipedia:
A call transfer is a telecommunications mechanism that enables a user to relocate an existing telephone call to another phone or attendant console, using a transfer button or a switchhook flash and dialing the required location. The transferred call is either announced or unannounced.
Unfortunately, Exotel does not have a call transfer feature yet! This is the guy responsible for writing code for it and he is currently still busy. There is no ETA this feature either as he is unable to tell us when exactly he will be free to write code for this. Specifically, he is investing a lot of his time on uptime & service quality related issues.