When you use an Aastra Handset with 3CX you may find that the correct Caller ID is not shown on the handset when you use Call Pickup or the call is transferred to your phone. This can be corrected by adding the following line in to your provisioning template for your Aastra handsets
sip update callerid: 1
This setting Enables or disables the updating of the Caller ID information during a call, by default the phone has a value of “0” assigned but by adding this line with the value “1” you force this setting to Enabled.