What actions are you performing on a Begin Call? In general its best to
use a subsequent event such as onCallDelivered or onCallEstablished as
the data associated with the call can be updated after the Begin Call,
especially if the call is being transferred from an IVR. Is there a
reason you arent using one of the other events?

That said, have you tried checking the calltype? The inbound call would
be type ACD IN. Since you are receiving a begin call on the transfer I
assume its a consultative transfer, so the calltype would be CONSULT or
AGENT INSIDE. The calltype values are in the CTI Server Protocol
reference under Constants and Status Codes.

There is no document showing calltypes are generated. The list of
calltypes is in the CTI Server protocol reference (GED-188). You will
need to test the calls in your environment to determine which calltype
is generated in different scenarios, though most of them are
self-explanatory.

I guess theres no harm in "start(ing) the process to open the
application" but be aware all the call data may not be present or may
change after the begin call so your application will need to be updated
with the call data using subsequent events like onCallDataUpdate.