You might try these strings with customers having a hard time connecting
Sometimes they work Sometimes they don't )%

Disconnects? Try S10=255
Diable V.90 MS=V34

Acer 
  AT&F2&C1&D2 

BestData 
  AT&F&C1&D2S11=60L3 
  AT&F&C1&D2 

Cardinal (Generic) 
  AT&F&C1&D2\N5 

Cirrus Logic 
  AT&F&W&W1 

Compaq Presario K56 VSC 
The only way to get this modem online 

is to put four commas after the phone number. 

Yes it sounds strange but it does work. 

Diamond Multimedia/Supra 
  AT&F2W2 

Gateway Telepath modems
  AT&F 

Generic 28800 bps 
  AT&F&C1&D2S7=60 

Hayes ACCURA/Optima
  AT&F&C1&D2 

Motorola ModemSURFR
  AT&F&C1&D2\K3 
  AT&F&C1&D2&K3\V1\N3L1S0=0 

Motorola VoiceSURFR
  AT&F&C1&D2\K3 
  AT&F&C1&D2&K3\V1\N3L1S0=0 

Mwave (only for IBM 28,800 models)
  "H%C/N*TH8 
  "H%C/NS28=18 

MaxTech 
  /N6 

Packard Bell Modem
  AT&F&C1&D2 

US Robotics Modems
  AT&F1&C1&D2&K0 
  &F1&C1&D2 

US Robotics Sportster 28.8 V.34
  AT&FX4&A1&B1&H1&M4&R2 

Wisecom Modems 
  &FE1L1V1&C1&D2S0=0S7=90 

Zoom 28.8 V.34(i) & (x)
  AT&F&C1&D2S95=1 

Zoom 56K Flex
  ATS202=32 

X2 Modems

  Cardinal Connecta 56K 
  Global Village Teleport 56 
  Practical Periferals 56K Data/fax 
  USRobotics 56K 

     Init String: AT&F1&K0&I0S32=32S15=128S27=64S32=34 
     Flash Upgrade: 
     Driver: 
     Notes: Yes, there are two S32=xxx in the above init string. I'm just reporting what a couple of people have said worked for them.