try +1 instead of 001.


from UM site
"How To Make Calls
Important notes: Always dial numbers with the full international dialing code. In
addition, after dialing with your UM (Riiing) SIM, you will be briefly disconnected and
receive a call back. Answer normally and wait for the call to be connected. If you
have problems making calls, try selecting another network.
1. Dial number with "+" country code (1 for the US), phone number
2. Press key
3. Your phone will display "Waiting For Call"
4. Wait for call back and pick up with your key like on a normal call
5. After a short while (10 to 30 seconds) the connection will be set and the phone
will start to ring on the other side.
There are not any special procedures to follow when receiving an incoming call. So,
to answer and incoming call, simply press the key.
Example: To call Switzerland, enter +41 1 311 3315, wait for your phone to begin
ringing and just pick it up!

Important Dialing Instructions!
From some countries it is CRUCIAL that you follow these instructions.
Instead of dialing normally you will need to dial using your phone’s menu. After
inserting the SIM in your phone you will see an option called “CALL/ANRUFEN” and
then select “DIAL/WAHLEN” and enter the number.
On Sony Ericsson phones this can be found under either “EXTRA” or the
“CONNECTIVITY” Menu.
On Motorola phones with a graphical interface look for an icon called “OFFICE
TOOLS” or “APPLICATIONS”.
On most Nokia and Siemens phones “CALL” can be found in the main menu or under
“EXTRAS”."