QuickIM 1.2

the author of this app says:

QuickIM is a fully featured instant messenger for Blackberry 7210, 7230, 7250, 7280, 7290, 7510, 7520, 7730, 7750, 7780 and similar devices (see the requirements and compatible devices section) supporting the public MSN network. It enables you to exchange and send instant messages to other phone and PC users from anywhere without paying any "per message" charge.