Speex and echo / ambient noise cancellation

Hello.  I'm new to Speex.  I see that noise cancellation is just one of
many features of Speex.  I'd like to learn more about this feature.

I've implemented an ios app on my iphone.  It's a call app.  The problem is
there is a lot of ambient noise transmitted to the other caller over SIP.
 Is there a way to use Speex to cancel this echo / ambient noise in
real-time streaming audio?  What would the CPU implications be if this in
fact possible with Speex?

Thanks,
Sam

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