dynamic ip's disadvantages for gsm modems how could it be solved ?

hi friends my problem is dynamic ip's disadvantages
hi I am to do connection between 2 sim900 modules.

if I know 2 moduls' IP THERE IS "NEMA PROBLEMA"

but ip's of these 2 moduls are dynamic so they are changing.

what can I do ??

my solution to this problem is here but its not working at all.

there is a web page named iprecord.php

in this page these things happen :

........./iprecord.php?name=A1&IP=123.456.789.963
........./iprecord.php?name=A2&IP=134.876.459.958

so I record their IP AT ONCE.and then systems trying this page:

........./requestip.php?name=A1

A1's IP=123.456.789.963

........./requestip.php?name=A2

A2's IP=134.876.459.958

this page search server and bring A1's and A2's ips.
and thas how they know their ip's.
BUT MOST IMPORTANT POİNT İS
when A1 's connction fail while conncting to other modem its try to connect again to gprs and its ip has changed so it is the most important problem for me what can ı do ????