RP3 tries to dial out even there is no dial tone. It should check for dial
tone before dialing out.
The default init string (ATZ) used by rp3 initializes your modem to its built-in
defaults, and the default dial string (ATDT) doesn't change this behavior.
If need be, you can change this by editing /etc/wvdial.conf and modifying
the proper "Init1" string to include "X4" (i.e., change it to "ATZ X4"),
which should force dial tone checking.