Wireless not GPRS

[I mate wa bas]

Dear Brothers

Can some one help me please;
I have i mate PDA2k , and use office wifi escpically for myself
But , I can access skype
throuhg wifi only , and once i opened Internet or
MSN it jump from wifi to GPRS,

Why it goes to GPRS and not stay in WIFI

Regards

And Thanks in Advance