This is not an authentication problem, as the connection fails far too early for that.
The critical error message is "LCP: timeout sending Config-Requests". Basically, pppd is unable to establish even a layer 2 connection with the peer. I'm not sure what the problem could be, but this caught my eye:
ttyUSB3<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK
ttyUSB3<*1>: Modem Identifier: ATI -- Manufacturer: "Micromax"
And then, a little further down:
ttyUSB4<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK
ttyUSB4<*1>: Modem Identifier: ATI -- Manufacturer: "Micromax"
So actually, your modem is detected on both ttyUSB3 and ttyUSB4. Do you have two such devices? Have you tried using ttyUSB4 instead of ttyUSB3?
Then there's this:
ttyUSB4<*1>: Speed 9600: AT -- OK
ttyUSB4<*1>: Max speed is 9600; that should be safe.
...which matches the "9600" parameter to pppd, but may not go to well with this:
ATDT*99#
CONNECT 7200000
That may be entirely cosmetic, although it would explain why pppd isn't getting any replies.
Are you sure the service you're connecting to uses ppp for authentication? I've seen a few setups where logins were done in plaintext before the ppp process started.
Have you tried connecting with a terminal emulator? You should see the ppp data from the peer as a lot of garbage characters on the screen as soon as you connect.
