Система CentOS 7. Интерфейс ppp0 поднимается через wvdial. Вот вывод messages -
May 27 22:21:24 gw ifup-ppp: pppd started for ppp0 on /dev/ttyUSB2 at 9600
May 27 22:21:24 gw kernel: PPP generic driver version 2.4.2
May 27 22:21:24 gw pppd[907]: pppd 2.4.5 started by root, uid 0
May 27 22:21:26 gw wvdial[926]: WvDial: Internet dialer version 1.61
May 27 22:21:26 gw wvdial[926]: Warning: section [Dialer Dialer] does not exist in wvdial.conf.
May 27 22:21:26 gw wvdial[926]: Initializing modem.
May 27 22:21:26 gw wvdial[926]: Sending: ATZ
May 27 22:21:26 gw wvdial[926]: ATZ
May 27 22:21:26 gw wvdial[926]: OK
May 27 22:21:26 gw wvdial[926]: Sending: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
May 27 22:21:26 gw wvdial[926]: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
May 27 22:21:26 gw wvdial[926]: OK
May 27 22:21:26 gw wvdial[926]: Sending: AT+CGDCONT=1,"IP","internet"
May 27 22:21:26 gw wvdial[926]: AT+CGDCONT=1,"IP","internet"
May 27 22:21:26 gw wvdial[926]: OK
May 27 22:21:26 gw wvdial[926]: Modem initialized.
May 27 22:21:26 gw wvdial[926]: Sending: ATDT*99#
May 27 22:21:26 gw wvdial[926]: Waiting for carrier.
May 27 22:21:26 gw wvdial[926]: ATDT*99#
May 27 22:21:26 gw wvdial[926]: CONNECT 100000000
May 27 22:21:26 gw wvdial[926]: Carrier detected.  Chatmode finished.
May 27 22:21:26 gw pppd[907]: Serial connection established.
May 27 22:21:26 gw ntpd[623]: Listen normally on 4 eth0 10.11.1.1 UDP 123
May 27 22:21:26 gw ntpd[623]: Listen normally on 5 eth0 fe80::67d:7bff:fe0f:e593 UDP 123
May 27 22:21:26 gw pppd[907]: Using interface ppp0
May 27 22:21:26 gw pppd[907]: Connect: ppp0 <--> /dev/ttyUSB2
May 27 22:21:26 gw kernel: cfg80211: Calling CRDA to update world regulatory domain
May 27 22:21:27 gw kernel: PPP BSD Compression module registered
May 27 22:21:27 gw kernel: PPP Deflate Compression module registered

May 27 22:21:54 gw network: Bringing up interface ppp0:  Failed to activate ppp0, retrying in the background
May 27 22:21:54 gw network: [FAILED]

May 27 22:22:04 gw pppd[907]: Connection terminated.
May 27 22:22:05 gw pppd[907]: Modem hangup
May 27 22:22:05 gw pppd[907]: Exit.

Если запустить из консоли руками - всё живет.

Настройки интерфейса:
DEVICE=ppp0
NAME=Megafon
WVDIALSECT=Dialer
MODEMPORT=/dev/ttyUSB2
LINESPEED=115200
PAPNAME=gdata
USERCTL=false
ONBOOT=yes
PERSIST=yes
DEFROUTE=yes
PEERDNS=no
DEMAND=no
IDLETIMEOUT=600

ЗЫ: Парадокс в том, что в другом регионе, с другой симкой, но тоже Мегафон, все работало.