Starting from Ubuntu 9.10, Network Manager uses ModemManager to communicate with mobile broadband (CDMA, UMTS and others) cards. Ubuntu 9.10 uses version 0.2 of ModemManager which most probably has some bug because of which few modems dont get recognized. ZTE AC2726, the modem which comes with PTCL EVDO, is one of the unfortunate ones. If you have Ubuntu 10.04 or later you can use the following procedure to connect to PTCL EVDO.
sudo apt-get install usb-modeswitch usb-modeswitch-data
Bus xxx Device xxx: ID 19d2:fff1 ONDA Communication S.p.A.
In the new Window enter firstname.lastname@example.org as user name and ptcl as password and click apply.
You are all set. To connect to this connection click on Network Manager icon in Taskbar. Select this newly created connection and click connect.