This trick works with Verizon. I'm not sure if it works with other carriers. If you want to insert a pause into a stored number on your phone, all you have to do is put a "p" between the numbers. If you want a hard pause, such that it does not continue until you hit the send button again, then put a "w" between the numbers.
This trick is usefull for accessing voice mail. You simply type the number to access your voicemail followed by a "w", and then your password. (ex. To program for your verizon cell phone voice mail 555-555-5555w#6666 where the 5's equal your cellphone number and the 6's equal your password.
I've tried this with serveral phones including a Kyrocera, Samsung i600, and Motorola Q.
Hope it works for you too