Modem: Ventel TrailBlazer (19200)
AT&FQ0V1S50=0S51=5S58=2S66=1S111=255X1

Modem: Ventel 9600 plus (38400)
AT&F&C1&D2\N3\Q3%F2S0=0S2=255&Y1

#Init string for USR Sportster 28.8 V.34 Modem
AT&F&H1&R2&C1&D2&B1&F1X2&K3&W

We have had some success using the above init string with USR Sportster 28.8k - V.34 Modems.

Using WINDOWS Terminal © or some other comm program, ensure that your modem is correctly connected by typing ATZ<ENTER KEY> on the command line. If your modem responds with OK then your modem is PROBABLY connected properly. Then type the above init string EXACTLY as it appears, followed by the <ENTER KEY>. Your modem should respond with OK, if it doesn't you typed something wrong, try again. Your default initialization string is now set, whenever you or your comm program send ATZ to the modem, it will reset to these settings.

Below is addtional info I found on other USR Models

         MODEL                  INIT STRING                  PORT SPEED
USRobotics Sportster V.34(US)    &F1X2&K3                       38400
USRobotics Sportster V.FC(US)    &F1X2&K3                       38400
USRobotics Dual 14400            &F&A3&B1&H1&K3&R2X7            19200
USRobotics Dual 16800            &F&A3&B1&H1&K3&R2X7            38400
USRobotics Dual V.34/V.FC        &F1&K3                         38400

Make sure hardware flow control is on (&h1 &r2 for US Robotics modems), turn on carrier detect (&C1) and follow dtr (&D2) and lastly the port rate (serial port to modem) should be fixed (&b1).
Check your particular modems manual for its settings.