Hi, all. I'm counting on this community for help on an issue with USSD messaging on the MC65 that was not present with MC5574. Find below a complete description from the partner's engineer. Attached also the routine developed by them at that worked with MC55. We double check the compatibility of this "wrapper" with WM6.5. We believe the cause of this is the different modem being used (2G vs 3G). The help requested is if somebody, from previous experiences, could point out a way to make the routine to work with MC65 as it did with MC5574. COMPLETE DESCRIPTION PROVIDE BY PARTNER:
Problem with USSD Messages using the MC65.  The MC55 works perfectly.

First of all, here is what USSD Messages are: Unstructured Supplementary Service Data (USSD) is a protocol used by GSM cellular telephones to communicate with the service provider's computers. USSD can be used for WAP browsing, prepaid callback service, mobile-money services, location-based content services, menu-based information services, and as part of configuring the phone on the network

We’ve been having problems with the way the MC65 handles USSD Messages; this messages are complicated to use, since they’re accessed through Microsoft’s Telephone API (TAPI) and they don’t have a .Net Namespace (which would make them easy to use in managed code). Anyway, we are using OpenNetCf.Telephony which is a wrapper for all unmanaged functions/classes in TAPI; it has done its job pretty well until now.

With this wrapper we have integrated the usage of USSD messages into our Sales Force application, basically what we do is send a special USSD message, this message creates a unique session at the server and the rest of the conversation (messages exchange) uses this session; messages travel from the device and back from the server until the purpose of the application is met. The problem we’ve had with the MC65 (which by the way is HSDPA) is that it is able to send the Initialization USSD message and it gets back the received confirmation from the server, immediately after this message, the server sends the response, this response is presented in a special pop up window on the handheld (we know it has been received) but the event that is monitoring all messages in TAPI doesn’t fire when this response arrives.

The exact same code works perfectly in any “GSM” Windows Mobile device, I’ve attached a sample in a RAR file (made in Visual Studio 2008 with the windows mobile 6 PRO SDK), anyone can try in any carrier by installing the SIM, and running the program, what will happen for sure is that any other carrier will respond “UNKNOWN APPLICATION” or another message to the USSD request, but even this error message is not captured by the TAPI in this device, we tried several devices, and the program didn’t work in either the ES400 and the MC65 (both HSDPA / 3.5G), so I guess it has something to do with the firmware of the Cell Phone/Modem.

We really need a solution to this problem ASAP since  we have various implementations that require this USSD messaging enabled, and since there are no MC55’s (or 2G GSM Devices) anymore we’re being forced to migrate to MC65’s, but without this working, we can’t!!!