I searched and read all messages including the words “call”, “calling”, “drop”, “dropping” in the “Jolla Phone : First experiences, Pros and Cons” thread, and could not find reference to these call dropping issues.
I only found this strange situation, with rejected calls with Telia (Sweden?) and VoLTE in particular when reception is very bad.
Which seems to be operator specific rather than the JP2601. I’d say you don’t need to worry too much. If the “first experiences” thread with 1000 messages does not say anything about call dropping, it’s not a common experience, probably a very local situation.