How can I create a phone dialler with WinAPI calls

You can use the following, courtesy of George Tasker, who originally wrote it.

Special thanks to Jon Hawkins who first posted it in the VFP forum.
[color blue]
#DEFINE WAITSECONDS 4
#DEFINE ID_CANCEL 2
#DEFINE MB_OKCANCEL 1
#DEFINE MB_ICONSTOP 16
#DEFINE MB_ICONINFO 64
#DEFINE GEN_READ 0x80000000
#DEFINE GEN_WRITE 0x40000000
#DEFINE CF_TEXT CHR(13) + CHR(10)

DECLARE INTEGER WriteFile IN Win32API;
[tab]INTEGER hFile,;
[tab]STRING @lpbuffer,;
[tab]INTEGER nNumberOfBytesToWrite,;
[tab]INTEGER @lpNumberOfBytesWritten,;
[tab]STRING @lpOverlapped

DECLARE INTEGER CreateFile IN Win32API;
[tab]STRING @lpFileName,;
[tab]INTEGER dwDesiredAccess,;
[tab]INTEGER dwShareMode,;
[tab]STRING @lpSecurityAttributes,;
[tab]INTEGER dwCreationDisposition,;
[tab]INTEGER dwFlagsAndAttributes,;
[tab]INTEGER hTemplateFile

DECLARE INTEGER CloseHandle IN Win32API;
[tab]INTEGER hObject

DECLARE INTEGER FlushFileBuffers IN Win32API;
[tab]INTEGER hFile

PROCEDURE DialNumber

LPARAMETERS PhoneNumber, CommPort

LOCAL lcmsg, lnport, lnwritten, lcmnd, lnstop

lcmsg = "Please pickup the phone and choose OK to dial " + PhoneNumber

IF MESSAGEBOX(lcmsg, MB_ICONINFO + MB_OKCANCEL, "Dial Number") # ID_CANCEL
[tab]lnport = CreateFile(@CommPort, GEN_READ + GEN_WRITE, 0, 0, 3, 0, 0)

[tab]IF lnport > 0
[tab][tab]lnwritten = 0
[tab][tab]lccmnd = "ATDT" + PhoneNumber + CF_TEXT

[tab][tab]IF WriteFile(lnport, @lccmnd, LEN(lccmnd), @lnwritten, 0) # 0
[tab][tab][tab][color green]* Flush the buffer to assure the data was written[color blue]
[tab][tab][tab]= FlushFileBuffers(lnport)
[tab][tab][tab][color green]* Wait to make sure it's been dialed[color blue]
[tab][tab][tab]lnstop = SECONDS() + WAITSECONDS

[tab][tab][tab]DO WHILE SECONDS() < lnstop
[tab][tab][tab][tab]DoEvents
[tab][tab][tab]ENDDO

[tab][tab][tab][color green]* Hang up command[color blue]
[tab][tab][tab]lccmnd = 'ATH0' + CF_TEXT
[tab][tab][tab]= WriteFile(lnport, @lccmnd, LEN(lccmnd), @lnwritten, 0)
[tab][tab][tab]= FlushFileBuffers(lnport)
[tab][tab][tab][color green]* Close up[color blue]
[tab][tab][tab]= CloseHandle(lnport)

[tab][tab]ENDIF

[tab]ENDIF

ENDIF

RETURN

ENDPROC