I have problem with my GSM modem, not the modem itself, but the service in my area is getting worse day by day.
Fortunately I have an old CDMA phone/modem lying around, the bad news is network manager couldn't handle CDMA connection with extra initialization command.
That's where KPPP comes in. It has simple interface and yet provides deeper configurations should you need it.

Starting the KPPP will open up this dialog box :

Click configure to (of course!) configure your connection, Basically you have to configure your account and which modem to use. The trickiest part is in adding new modems. You should now where it is located e.g.: /dev/ttyACM0 for Nokia Phones connected via data cable. I don't know easy way to know this, yet.
You can add extra initialization command in Modems -> New... -> Modem -> Modem Commands. 

After that. all you need to do is click Connect.

And here's how KPPP at works :

keyword : KPPP, CDMA, Nokia Phones