Im- : A form of the prefix in- not, and in- in. See In-. Im- also occurs in composition with some words not of Latin origin; as, imbank, imbitter.

Example:


Taxonomy
SMS, instant message, PC calls, download, yahoo messenger, windows live messenger, iPhone, file sharing, Send text messages, instant messenger, instant messaging, chat rooms, mobile phones, shortcut, System requirements, Internet Explorer, Explorer 6.0, Mozilla Firefox.

Defination from the web:
... Friends are an instant away on Yahoo! Messenger for the Web. Get Started. No download required to IM with friends ...