Instant Messaging for Critical Alerts in a AD Domain

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.NET3.5

.NET

Dear Colleagues:

I need some help about an application I´ve got to develop, please.

Description: our Call Center need to send instant and critical messages to users, and/or groups in our AD domain.

Main requirements are:

(1) Our Call Center need to be absolutely sure messages are read by all users.
(2) No applications on client machines.

Possible solutions I´ve checked:

(1) NET SEND Wrapper: discarded due to NET SEND is "deprecated".
(2) MSG.EXE: this tool is not really designed to mass message people.
(3) Developments over OCS is also discarded: I´ve not found a way to make Communicator windows pop up to foreground in case a Call Center conversation. Toasts (supertoasts and similar) are not enough.
(4) Addins to Communicator: only for LYNC 2013, but we´re still with OCS R2 and looks like for a long time to change.

Can you help me? Just need some few tips and I think I´m able to dig down on them.

Thank you very much in advance.

Best regards,
Fernando.