How to-connect Huawei E220 USB modem

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This is my first how to and I hope it will be useful.
I had a problem to connect Huawei E220 USB mobile modem. I used the thread "http://ubuntuforums.org/showthread.php?t=843973" .
Then when I used the terminal with
$ wvdial Defaults

I obtained the following message

Warning: Could not modify /etc/ppp/pap-secrets: Permission denied
and the PPPD aborted.

I came over this with the command
$ sudo chmod a+rw /etc/ppp/pap-secrets

Then I repeated the "$ wvdial Defaults", successfully,

I restored the original permissions with:
# chmod a-rw /etc/ppp/pap-secrets
# chmod u+rw /etc/ppp/pap-secrets

I hope you have found this helpful.