Connectivity with PDA

Hi all
Iam working on the SIP mode .I wanted to make a call from my linux server to the smart handset phone (PDA) also sip based which is ported with the WIN CE . I configured the setting perfectly alright but when i made the call it is not happening .Then i ping from my linux server to the smarthandset phone it is not pinging.
One intersting thing i like to mention here is that whenever iam pinging from any of the linux system it is not pinging .But if iam pinging from the windows XP to the smarthandset it is getting ping .

Does anyone has got any suggestion