17-03-2012 10:33 AM - edited 17-03-2012 10:37 AM
Taken from SGS2 user manual:
To make a multiparty call (conference call), make or answer a second call and select Merge when connected to the second party. Repeat to add more parties. You must subscribe to the multiparty call service to use this feature.
Since you have used the feature on your previous phone you should already have this enable on your account.
AT+T in the states have made a small demo video showing how to do it.