Saya menggunakan ubuntu 8.04 dengan default installasi tanpa menggunakan repo tambahan atau yang lain , di tes menggunakan modem sierra(875 USB) dan huawei(E220 USB) tanpa setting tambahan modem langsung kedetek.
Yang perlu dilakukan disini hanya menambahkan script dial up untuk pppd yang sudah terinsall di ubuntu saat awal instalasi

Sebelumnya pastikan sudah sebagai root , dan masuk ke directory /etc/ppp/peers/
buat file sesuai dengan nama dial-up yang diinginkan , disini sebagai contoh menggunakan dialup provider telkomsel , maka saya akan membuat file “tsel” (nama file terserah :P)

tsel

-detach
lcp-echo-failure 0
/dev/ttyUSB0
2048000
debug
defaultroute
usepeerdns

#ipcp-no-address
#ipcp-no-addresses
ipcp-max-failure 4
ipcp-accept-local
ipcp-accept-remote

# AUTHENTICATION
# If noauth works, use that, otherwise you have to pass
# the user name and password. This is an example of a
# standard Cingular user/pw combo

#noauth
user
password 

crtscts
lock
connect '/usr/sbin/chat -v -t6 -f /etc/ppp/peers/tsel_chat'

kemudian buat file tsel_chat yang berisi :

# Connection script for Sierra Wireless GSM/UMTS modems
# Note: This demo script is setup to work on the Cingular EDGE network
#
SAY 'Starting Sierra Wireless GSM connect script...\n'
SAY '\n'

#######################################
SAY 'Setting the abort string\n'
SAY '\n'
# Abort String ------------------------------
ABORT 'NO DIAL TONE' ABORT 'NO ANSWER' ABORT 'NO CARRIER' ABORT DELAYED

#######################################
SAY 'Initializing modem\n'
# Modem Initialization
'' AT
OK ATZ

#######################################
SAY '\n'
SAY     'Setting APN\n'
# Access Point Name (APN)
# Incorrect APN or CGDCONT can often cause errors in connection.
# Below are a bunch of different popular APNs

#REG:\s1 AT+cgdcont=1,"IP","proxy"
#OK     'AT+CGDCONT=0,"IP","proxy"'
#OK     'AT+CGDCONT=1,"IP","proxy"'
#OK     'AT+CGDCONT=2,"IP","proxy"'
#OK     'AT+CGDCONT=0,"IP","ISP.CINGULAR"'
OK     'AT+CGDCONT=1,"IP","telkomsel"'
#OK     'AT+CGDCONT=2,"IP","ISP.CINGULAR"'

#######################################
SAY '\n'
SAY     'Dialing...\n'
# Dial the ISP, this is the common Cingular dial string

OK ATD*99#
CONNECT ''

sesuaikan isi dari file diatas dengan properties dial-up masing-masing provider

untuk mulai melakukan dialup , ketikkan perintah berikut pada console

pppd call tsel

jika berhasil maka akan muncul string sebagai berikut

kucing@ferrari:~$ pppd call tsel
speed 2048000 not supported
Starting Sierra Wireless GSM connect script...

Setting the abort string

Initializing modem

Setting APN

Dialing...
Serial connection established.
speed 2048000 not supported
using channel 3
Using interface ppp0
Connect: ppp0 <--> /dev/ttyUSB0
sent [LCP ConfReq id=0x1  
 ]
rcvd [LCP ConfReq id=0x8   
 ]
sent [LCP ConfNak id=0x8 ]
rcvd [LCP ConfAck id=0x1  
 ]
rcvd [LCP ConfReq id=0x9   
 ]
sent [LCP ConfAck id=0x9   
 ]
sent [LCP EchoReq id=0x0 magic=0x720a6119]
sent [PAP AuthReq id=0x1 user="password" password=]
rcvd [LCP DiscReq id=0xa magic=0xc0d19b]
rcvd [LCP EchoRep id=0x0 magic=0xc0d19b 72 0a 61 19]
rcvd [PAP AuthAck id=0x1 ""]
PAP authentication succeeded
sent [CCP ConfReq id=0x1   ]
sent [IPCP ConfReq id=0x1    ]
rcvd [LCP ProtRej id=0xb 80 fd 01 01 00 0f 1a 04 78 00 18 04 78 00 15 03 2f]
Protocol-Reject for 'Compression Control Protocol' (0x80fd) received
rcvd [IPCP ConfNak id=0x1  ]
sent [IPCP ConfReq id=0x2    ]
rcvd [IPCP ConfNak id=0x2  ]
sent [IPCP ConfReq id=0x3    ]
rcvd [IPCP ConfReq id=0x4]
sent [IPCP ConfNak id=0x4 ]
rcvd [IPCP ConfRej id=0x3 ]
sent [IPCP ConfReq id=0x4   ]
rcvd [IPCP ConfNak id=0x4   ]
sent [IPCP ConfReq id=0x5   ]
rcvd [IPCP ConfAck id=0x5   ]
rcvd [IPCP ConfReq id=0x5]
sent [IPCP ConfAck id=0x5]
Could not determine remote IP address: defaulting to 10.64.64.64
Cannot determine ethernet address for proxy ARP
local  IP address 10.129.27.19
remote IP address 10.64.64.64
primary   DNS address 202.3.208.10
secondary DNS address 202.3.210.10
Script /etc/ppp/ip-up started (pid 6152)
Script /etc/ppp/ip-up finished (pid 6152), status = 0x0