Activate the "Call Waiting" feature! The current call will be put on hold to answer an incoming call.
After you have finished the current conversation you can return to the previous call easily. It's also possible to put the active call on hold, dial another number and after you will be able to talk back to your first call. Please note when the feature is active and you put the call on hold, both calls will be billed. Call Waiting can be disabled in your cell phone, refer to the manual of your phone for more info.
LemonSIM in your phone you can call any mobile or landline network in any EU country at the rate of 0.15 €/min!