The Nokia 3100b cellphone model was developed from the Nokia 6100 model and was meant to succeed the Nokia 3510i model. The 3100b was released in June 2003 with voice-recording capability in addition to all of the original features of the 3510.
The Nokia 3100b model is the North American version of Nokia's line of 3100 phones. To verify that you have the Nokia 3100b, first turn off the device. Then remove the back cover and remove the battery. Look for "Model 3100b" written above the three bar code lines.