Getting custom forms data stored in Exchange from VB.Net

Hi. We have an custom apponitment form, with some text fields in P2. From
VB.Net, we can view the data of the appointment of the general tab, but we
can't access to our custom tab. We think that the problem is that our
custom form tab does not appear in the OWA, and we are accessing to data
from
VB.Net via //exchangeServer/exchange/user/calendar. The question is: there
is any way to access to data stored in custom form in exchange from VB.NET?

Thanks.