Re: i sent SMS from my n900 but message is received as MMS on wife's cliq ???
 

There is an sms setting on most phones that enable the option to send sms replies through the sms service center of the person who send you the sms.
I'm not saying it will certainly fix the problem, but it could explain why replying to an sms fails and sending a new one works like a charm.

Check if you can find such a setting on your wifes phone.

Goodluck