Change the settings to :
Phone Number: xxx-xxx-xxxx
Dial Mode: TONE
Bits Per Second: 2400
Parity: NO
Data Bits: 8
Stop Bits: 1
Xon/Xoff Control: ON
Signal Line Control: NONE
Local Echo: OFF
Auto Linefeed (Feed): OFF
Auto LineFeed (Send): OFF
CR>CR/LF (PN-8510MDS ONLY)
Receive OFF
Send OFF