Finally; it took until Windows Mobile 5.0 but now it is there - Microsoft's Windows Mobile 5.0 now supports simultaneous data connections (e.g. W-LAN and GPRS/UMTS) including seamless handover between both connection types. While GPRS is at least (depending on your country) always available, W-LAN isn't but only at home, in the office or at selected HotSpots.
On the other hand, in most cases W-LAN is way faster and in most cases cheaper than GPRS (or UMTS) and therefore a W-LAN connection is preferred in most cases.
With the seamless handover "dual-connection" you can stay connected via GPRS, for example to MSN Messenger or your E-Mail server. However, as soon as you reach a (recognized) W-LAN access point, Windows Mobile 5.0 connects to this connection in addition and switches the internal data routing from the WAN (GPRS or UMTS) connection to the LAN (W-LAN/Wi-Fi) connection:
As you can see above, first I was connected with the O2 GPRS network only. However, as soon as I've reached my apartment, the device recognized my home W-LAN network and connected with it in addition.
A short check against my web-server confirmed that I was accessing the::unwired through my DSL line now instead of the previously used GPRS data connection.
If you leave the W-LAN covered area again, the device disconnects from the known W-LAN and continues seamlessly with the previously used GPRS (or UMTS) connection and isn't dropping your current online services (such as MSN Messenger).
As I said, this is pretty handy for always on services like MSN Messenger, E-Mail (or FTP) but also useful to get the full GSM service-support while you are connected with a W-LAN network. For instance, right now with Windows Mobile 2003SE, you will not receive MMS messages while you are connected though W-LAN (all you get is the notification that a new MMS is waiting for download) as well as you are not able to send MMS messages while connected because 2003SE supports one connection only. This means that you have to download waiting MMS messages later as well as you have to send them later by pushing you MMS client to send them now.
Now, with Windows Mobile 5.0 you don't have to think about this anymore as well as you will always be able to use the cheapest (and fastest) connection type for your Internet connection.
As far as I've seen W-LAN always have the higher priority over cellular connection types which means a Windows Mobile 5.0 equipped Pocket PC is always using the faster W-LAN connection over a slower (and in most cases more expensive) GPRS and/or UMTS connection.
Pretty cool! :-)
Cheers ~ Arne