The Zapp Handset may be configured to work with any terminal application (like Hyperterminal). 

All you have to do is:
a. set the Zapp Handset speed at 19200
b. configure the Handset as "Standard Modem 19200" (in your operating system)

You may use the usual AT Commands like:

ATZ
Initialize the Modem

ATDT 
modem dial string
like: ATDT0788111111

ATS0=1
Modem Auto Answer String
(1 means one ring)