Connecting using a GSM mobile broadband USB modem succeeds but there
are errors during the PPP handshake.  When the “debug” option is
uncommented in /etc/ppp/options as well as the “-detach” option, the
ppp logging is no more verbose than without those options. They seem
to take no effect. Is wvdial launching pppd in a way that interferes
with parameters in /etc/ppp/options?

This is the output both with and without debug info enabled:

/var/log/messages:

  ===8<------------------------------
  $timestamp $host pppd[84797]: pppd 2.4.9 started by $user, uid 0
  $timestamp $host pppd[84797]: Using interface ppp0
  $timestamp $host pppd[84797]: Connect: ppp0 <--> /dev/ttyUSB0
  $timestamp $host pppd[84797]: LCP: timeout sending Config-Requests
  $timestamp $host pppd[84797]: Connection terminated.
  $timestamp $host pppd[84797]: Modem hangup
  $timestamp $host pppd[84797]: Exit.
  ------------------------------>8===

/etc/wvdial.conf:

  ===8<------------------------------
  [Dialer Defaults]
  StupidMode = 1
  Modem Type = Analog Modem
  Baud = 460800
  New PPPD = yes
  Modem = /dev/ttyUSB0
  ISDN = 0
  Init1 = ATZ
  Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0

  [Dialer Orange]
  Init3 = AT+CGDCONT=1,"IP","mworld.be",,0,0
  Phone = *99#
  Mcc = 206
  Mnc = 10
  Username = ''
  Password = ''
  Carrier Check = off
  ------------------------------>8===

/etc/ppp/options:

  ===8<------------------------------
  asyncmap 0
  auth
  crtscts
  lock
  hide-password
  modem
  debug
  -detach
  nodetach
  lcp-echo-interval 30
  lcp-echo-failure 4
  noipx
  ------------------------------>8===