Modify the email launcher API to add an attachement

Having an orientation lock is a must have for the next update. Something so simple. Why it was not included when WP launched is beyond me. The phone is frustrating to use in bed or on laying on the lounge.

We need to see more media formats supported......

Bring back categories for Outlook integration. Including Tasks, appointments and contacts

Now the SMS delivery reports come in as separate text messages which is very inconvenient. Wouldn't it be nice if - when enabled - a delivery report was shown right next to the message as an icon (approval mark or something)? You would instantly know that the SMS was delivered and if you wanted further details (delivery time) you just click on it.

Allow users to choose if they want the "call/don't call" prompt dialog when an app invokes PhoneCallTask.

Fast dialing apps are killed by this limitation.

The same way a user can grant for background tasks, he could grant the app permissions to make direct dialing.

An option to choose between vibrate on keypress or sound on keypress
I love to type with vibrating keypress

I think WP7 contains a superior user interface to other mobiles OS's.
However the screen lock code seems out-of-date and sub-par to the rest of the interface. Android allows you to setup a graphical pattern, for example, while WP7 only allows you to enter a PIN code.
A graphical pattern is more practical and user friendly that a PIN code.
I don't think this is a difficult thing to implement and would improve the user experience.

The current auto sync with skydrive compresses pictures before uploading. This way still no real backup is made. Since skydrive offers 25gigs more then enough space is available for backing up in full size. Create an option to 'only upload to skydrive when connected by WiFi' and an option to choose to compress or not.

In the call log, we can see multiple entries for the same contact. Instead, just show the latest activity.
And show the previous entries, when clicked on the latest entry!!

In my humble opinion, the Windows Phone is the best gaming phone on the market today. The connection with XNA and Xbox are limitless. I would love to see a Windows Phone that had real controls. If Microsoft or one of the manufacturers created a phone like that, it would make the experience even more awesome! Apple made a mistake of blocking any type of gamepad control for their phone. I would love to see Microsoft follow the path of Xperia Play and embrace this type of phone!

It is late and I have forgotten to load the battery of my thirsty Windows Phone. I plug it into the power outlet and THEN it plays this stupid sound, my wife wakes up and I am mad about it. I then have to mute the sound every time I have to load the phone. Of course I sometimes forget to crank up the loudness afterwards so I will not hear the morning alarm. So please make it possible to disable the sound played when the WP7 is connected to the power outlet.

Support for multiple calendars, e.g. Multiple Google Calendars from one Google account, would be very useful.

If you activate a pin for the phone Kids Corner automatically gets a pin too. This means that you as a parent have to unlock the phone for your child. (Or give them the pin which kind of defeats the purpose.)

Feature suggestion: I would like to be able to set "no pin" in the settings for Kids Corner. Additional feature option would be to specify a different pin for Kids Corner (1234) :)

It makes no sense to have a pin for Kids Corner if you have, say, only configured a few games in that area for your child!

Please provide Access for Emails to BackUp the content to allow the windows phone Developers to implement an application regarding Emails.

having come from iPhone and loving my WP7.5 device, i miss the threading of calls. example you call Mr. Smith 6 times and he calls you twice, have them collapsed into a list that you can expand, this reduces the size of the list and lets your be more organized. searching by missed, Called, and all would be great at well.

Allow the user to send video in an MMS message. In mango, only sharing via email is supported.

Currently the only playlist option in Zune is to save a "now playing" list as a playlist. It is frustrating, however, when you can't add a newly downloaded song to an existing playlist.

My corporation's WIFI SSID is not broadcast--as is not uncommon practice. Being unable to enter that SSID prevents me from using my WP7 phone as a corporate device.