BT is not going to work with Winlink Express easily. You can connect over TCP on the WiFi side. Set up the packet parameters to connect to the DigiPi as KISS over TCP to talk to Direwolf. In my example below, I'm pointing to the IP of the DigiPi (which you can get from the display if you have one), but digipi.local may work too depending on how your network is set up:
For phone applications, WoAD may find the DigiPi over BT, but that will not work on iPhone. In both cases, I would again use WiFi. Direwolf advertises itself on the network, and RadioMail finds it easily on iOS. I believe the same is true with WoAD, but haven't tested that.
BT is not the best option.
-Scott, NS7C