3G dongle switch to modem after the network interfaces loaded

Question

I have a Raspberry Pi with a 3G Dongle connected. I want to automatically switch in modem mode + load the ppp interface during the boot.

I use usb_modeswitch to automatically switch in modem mode during the boot and it works.

And wvdial is well managed if it launches like it after the boot: sudo wvdial ppp0. I can ping the world! (OK just IPs and domains)

The issue is the interfaces network are loaded before the modem switch in boot process... As you can see in the syslog file (check dates and hours):

Feb 11 19:18:07 raspberrypi logger: /etc/ppp/wait-dialup-hardware: ERROR timeout waiting for required device /dev/gsmmodem

Feb 11 19:18:09 raspberrypi logger: usb_modeswitch: switched to 05c6:6000 on 001/005

I have tried this solution to force to wait the dialup hardware. Waiting the /dev/gsmmodem is mounted but it doesn't work.

My /etc/network/interfaces file:

auto ppp0
   iface ppp0 inet wvdial
   provider ppp0
   pre-up echo "3G dongle starting..."
   pre-up /etc/ppp/wait-dialup-hardware gsmmodem 30
   post-up echo "3G (ppp0) is online"

My /etc/ppp/wait-dialup-hardware file:

#!/bin/sh  

INTERFACE="/dev/$1"
MAX_SECONDS_TIMEOUT=$2

dsec=$(( MAX_SECONDS_TIMEOUT * 10 ))
retry=0 
while [ "$retry" -le "$dsec" ]; do
   if [ -c ${INTERFACE} ]; then
      echo "$0: OK existing required device ${INTERFACE} (in $((retry / 10)).$((100 * (retry % 10) / 10)) seconds)"
      logger "$0: OK existing required device ${INTERFACE} (in $((retry / 10)).$((100 * (retry % 10) / 10)) seconds)"
      break
   else
      sleep 0.1
   fi
   retry=$(( retry + 1))
done
if [ ! -c ${INTERFACE} ]; then
    echo "$0: ERROR timeout waiting for required device ${INTERFACE}"
    logger "$0: ERROR timeout waiting for required device ${INTERFACE}"
    exit 1
fi

How can I fix that?