When using rp3-config to configure my ISP connection, pressing the 'Debug' button the first time resulted in: ATZ AO: 0 (I think that's what it said) Modem initialisation failed Subsequent attempts were fine. Perhaps the modem detection needs to make sure that the modem's finished what it was saying?
RP3 has been deprecated and removed in the latest releases and Red Hat Linux 6.2 is about to be end of lifed. THe problem would be listed as 'Fixed by removal' if there was such a flag.