- Distance of the provider from their home.  (anything over 2-3 miles 
  depending on the phone lines can dramatically bring down speeds.)

- Some phone lines can not support that much data (older phone lines)

- Make sure the Modem Enumerator is using an IRQ above 9. 

- Some phone companies use a line compression unit which limits the 
   amount of data that goes through the phone lines so that they don't 
   overload.  (Places of high volume usually but not necessarily)
   Usually known by phone companies as slick concentrators.
- Make sure they are using the new phone cable (possibly the one
  provided with the modem)  When a cord gets old, there is more line noise
  therefore a decrease in speeds. 

- If it is a softmodem, do they have at least 512k L2 Cache? Celeron chips
 do not have these.  One way of verifying is when the computer is booting
 up look at its specs on the first screen.

- Go to the My Computer Icon and Right Click.  Select Properties.
  Click on the Performance tab and Select the Graphics button.
  Bring the Graphics Acceleration down to 1 knotch. (this brings down the Video Cards CPU usage to allow 
   the modem to use more)

-For the Softmodem an Intel 166mmx, AMD a 233, Cyrix a 266 are needed. 
 These are just the minimum requirements.  The more ram and speed you have the better
 the response from the modem.
- If through the path that your signals are being routed to the ISP has more
  than one analog to digital converter.  Sometimes these paths may
  change through out the day depending on phone line congestion which 
  could account for different speeds from night to day.  Not all routes
  change throughout a day.  Please phone the phone company and give them
  your address and the address of your ISP and count the amount of
  converters in between.  With more than one it can throw it down a lot 
  more than half sometimes.

- Have them do the USR test line to see if their phone lines are capable of
  V.90 connections.

- See if they have anything hooked up between the computer and the
  wall jack which could cut off some of the signals.

OTHER PHONE LINE FACTORS THAT CAN SLOW SPEEDS DOWN OR PREVENT V90

LOAD COILS - These are found primarily in long wire lengths to improve
                          the quality of a voice call. 
                          They will not necessarily prevent V90 but they can 
                          reduce the speed of your v90 
                          connects.

PADS - These come in primarily two forms: digital and analog.  Both types
            are used to balance the volume between different lines, so that
            the volume of the voice call is the same on both ends and within a
            reasonable range.  With a digital pad, the digital data is
            manipulated to adjust the volume.  There may be a reduction in v90
            speeds with this, but it should not prevent V90 connections.  With
            analog pads, the digital data is converted to analog where the
            volume is adjusted and then converted back to digital.  This will 
            prevent a V90 connection since there is more than one analog 
            section in the path.

WIRING - In the home or in the phone company's area, wiring can also 
                  hinder V90 connections or speeds.  If the lines are old and are 
                 subject to a lot of interference that may reduce your V90 
                 speeds.
 

-The less Applications running, the better the performance for a PCI 
  modem.

All this information can be verified at www.56k.com