blackberry - echoing voices...?

[joko]

ive a curve 8900...and a fewpeople have told me that when they have phoned me it has had about a 1-2 second delay on their voice - it sounds fine to me but they can hear a pretty long echo delay on their own voices...

any ideas why? how can i stop this?

ive checked i didnt have it on speaker phone by accident.

Thanks