don't forget there might be other things which can slow your modem down. Eg: extension cable, Fax machine, double adaptors, message bank, if you are in the rural area, make sure you turn off your electric fence.. alternatively, if none applies, reinstall modem driver.. if it still doesn't work, get yourself a MOLDS test from your phone company eg: Telstra.
Try upgrading your firmware or modem driver from the manufacturer's website.
Don't use +ms=11 as that will slow down your modem to v34.
I suggest search for the proper modem string from the net..
Iprimus tech advise is a no no!
Ps: Telstra OWNZ iprimus.