Sony Ericsson does not allow + sign in textbox!

I am currently developing a J2ME application for Sony Ericsson phone.
In the application, I have a texbox which only allow users to input numbers and certain signs as how you would enter your normal phone numbers.

This is the code that I use:

TextBox my_box = new TextBox("Enter here", "", 50, TextField.PHONENUMBER);

However, I faced a problem in Sony Ericsson as I could not enter a plus sign(+).
I checked tried in Nokia S40 and it works!
If you realised in Sony Ericsson, the key pad to input the + sign is the same as with the number 0.
So when you tried to input the + sign, it is always the number 0 that appears. :(

I then realised that there's no bug actually!
To insert a + sign in Sony Ericsson, one should press on the 0 longer. :)