Windows 7: Can't allocate drive letter

Hi
Posted this on Vista Forums but nor reply as yet. I think any reply regarding 7 would probably work for Vista anyway.
I have Vista Home Premium and am running as administrator. I have a portable device attached via USB. It is connected fine and Windows Explorer can see it but has not allocated a drive letter. I have not got any other devices attached and I don't think the problem is a conflict with another letter. The Device Manager has got See Hidden Devices switched on and it can see it - it is listed under Portable Devices.
I want to allocate a drive letter. All the postings I can find anywhere say that can be done by:
Command Line - but only as far as I can see, to re-allocate a drive, and this hasn't got one to re-allocate.
Disk Management - The device doesn't appear there at all. All the postings I can find say it will be there and all I have to do is click on it and allocate a letter, but this doesn't appear at all.

Try re-starting your OS with the device in place then go back to "Disk Management" your portable h/ware should have been recognized by your OS. Go to change drive letter & paths for your particular item if none has been allocated automatically.

You don't mention what kind of device it is. If it's an MTP device - e g mp3 player - I don't think they are assigned drive letters. At least my Creative Zen isn't.

Hi Both
I have many times tried restarting with the device attached and not attached, but the result is the same - no results.
The device is a mobile phone. It can take a memory card but it's the phone's internal memory I'm after.
I can switch the phone's PC connections between Media Player mode and Mass Storage mode, but the results are the same - and in both cases that is whether I do or don't have a memeory card present.
In Device Manager /Properties/Details, there are so many values present, I can't list them all and they mean nothing to me.