A year ago, I purchased a Samsung Blackjack through my carrier, AT&T.  I had previously been using a Cingular 3125 and had greatly enjoyed being able to voice dial with my BlueTooth headset and was very disappointed to discover that voice dialing would not work with Windows Mobile 5 and the Blackjack.  At the time, I did some research and found there was a throng of Blackjack owners who were putting there hopes on an upgrade to Windows Mobile 6 that Samsung and AT&T were going to provide at some point in the future.  For months, I've periodically checked around to see if an upgrade had been released.  Lo and behold, I checked, yesterday, and found that an upgrade was available on Samsungs site, here.  I quickly installed the upgrade, but found that Voice Command 1.6 running on Windows Mobile 6 STILL would not support voice dialing.  Guess I'll have to upgrade to the Blackjack II to get that functionality back :-(

Regarding the upgrade, I found it to work as advertised and adds the ability to edit Word, Excel and Powerpoint files on the device.  However, the directions instruct you to install the modem drivers (they allow your PC to talk to the phone without Activesync) and then use Activesync to back up any data from your device.  After installing the drivers, connecting and disconnecting the phone - attempting to get the device to connect through Activesync slowed my PC to a crawl and required a reboot to remedy.  I'd suggest you perform any backups PRIOR to installing the modem drivers to prevent this problem.

So, as I said, I have written this Smartphone application and was toying with the idea of either making it shareware or selling licenses on sites like Handango.  After thinking about it for a while, I realized all of the following had to be considered for this type of application.

1. Signing the application - Bottom line, here, is that any application that's installed on your Smartphone will need to be signed with a certificate that Either Microsoft or the phone's carrier has installed on the device.  You basically have two options, here.  First of all, you can go with Microsoft's Mobile2Market program.  With this program, you submit your application to a third party for scrutiny and once approved, you are issued a certificate with which to sign your application and you have the privilege of displaying the associated Made for Windows Smartphone icons on your site and packaging.  Plus, your product gets listed in Microsoft's / your OEM's catalog.  The other option, is to just purchase a certificate, like this one, with which to sign your application and installer.  The second option is cheaper, but it's up to you to decide which would be the better buy for you.  More on your options, here. 
2. Data Storage - Putting myself in the place of a consumer obtaining an application for my mobile phone, I'd prefer to be able to purchase, download and install the application and have it just work from then on.  With an application like the one I have written, data is being input into the application over a long period of time.  Where does this data get stored?  I could store it on my phone for a while, but before long there wouldn't be space enough for all my data.  There is always the Sql Server solution where data is stored in a mobile database on the phone a periodically synced to a full blown Sql Server when the phone is synched with a computer on the network.  Question here, though, is who's going to set that infrastructure up and configure the phone to connect with it properly?  This basically means the application has to come with some form or storage "in the cloud" that it knows how to connect to.  The storage space and maintenance of the hardware and software involved represents an additional cost whether we're talking about an aspx front-end or asmx.
3. Bandwidth Usage - Different cell providers offer varying qualities of access to the internet at various prices.  Can I assume that the cost of this type of access is negligible for the user of the application?  I'm thinking the safest bet is that I cannot.  I, therefore, have to be mindful that bandwidth usage is at a minimum; that calls to the web are not more frequent or chatty that necessary. 

I've been working on some infrastructure for my contracting business.  There are a lot of things that need to be tracked when you run your own business and for me it seemed that whenever I remembered something needed to be recorded I wasn't near a computer.  However, I always have my mobile phone (Samsung Blackjack) near by and it made sense to me to write an application that allowed me to log things like time, mileage and the like from my phone.

Architecture
I could have gone the route of creating a web site for this purpose, but instead I decided to create a SmartPhone application that called web services on my server, at home.  This way, if I ever decide to write a Windows Form or Web application front end, I can use the same web services and not have to recreate the logic they provide.  The web service methods give me all the CRUD functionality I need to manipulate the data I'm storing, so all the UI code on the phone needed to do was collect data and call the web service for storage.

Writing the mobile application was very straight forward.  I set a web reference to the web services I'd written and coded against the generated proxy.  Getting used to the mobile controls and the bits of functionality not provided in the compact framework were the biggest challenges, but nothing major at all.

Lessons Learned
Getting an internet connection in the emulator
After I had written a bit of code, I was eager to see it run.  I clicked the Start Debugging button on the Visual Studio toolbar and after prompting me for a target to deploy to (choose the emulator), an instance of the emulator was created and my code was deployed to it.  When I tried exercising some code that made a web service call, a transport error was raised.  I then tried to open pocket IE on the emulator and browse to an internet address, but got a message saying that I needed to configure my network settings on the phone.  After some searching, I figured out how to set it all up.  First, make sure you have ActiveSync installed and running.  Then, right-click its tray icon and choose "Connection Settings" from the context menu.  Make sure the check box for "Allow connections to one of the following:" is checked and select "DMA" in the combo box. 

In Visual Studio, go to the Tools menu and select "Device Emulator Manager...".  When the dialog opens, right-click the entry for "USA Windows Mobile 5.0 Smartphone R2 QVGA Emulator" and select "Connect".  This will open an instance of the emulator.  Next, right-click the same entry again and select "Cradle".  At this point, ActiveSync should detect the emulator and treat it as it would a physical phone plugged into the USB port of the PC.  Once you go through the connection wizard, you should have access to your PC's internet connection from the emulator through ActiveSync.

Deploying to the SmartPhone
Once my mobile application was unit tested, I was ready to deploy it to my phone.  I connected the phone to the PC, right-clicked my mobile project in Visual Studio and selected "Deploy".  The phone popped up up several dialogs asking me to approve the installation of several files on my phone.  I approved all of these, but the deployment still failed.  The reason stated indicated that there were some certs needed on my phone to deploy for development.  To get past this error, copy the file ...\Program Files\Microsoft Visual Studio 9.0\SmartDevices\SDK\SDKTools\VSDCerts.cab to your phone.  Then, on the phone, open the cab file to install the required certificates.  The deployment should succeed after this is done.  Of course, if you're developing an application for distribution, you'll want to properly sign your application instead of taking this short cut.