For iPhone, to insert a pause between the  gateway 1800877734 and phone number, please follow the steps below. 

For Android phone, to insert a pause between the gateway 1800877734 and phone number, please use the COMMA key: " , "
One comma = approximately 2 seconds pause. Try insert one comma first to test it out and add more commas if necessary.
Below is how I input and see a contact number.

The first contact is for sending sms to Najib.
The second contact with NT extension denote a pre-programed Nitetone voice call to Najib.

Contact Najib:
Mobile: +601234567890

Contact Najib NT:
Mobile: 1800877734,0123456789