Please keep this page open as the instruction set is a bit long.
dial *#61# call
this informs you of the forward to number and ringer length (likely 20 seconds)
next, dial **61*+xxxxxxxxxxx*11*yy call
for xxxxxxxxxxx use the forward to number you retrieved, you must start it with +
for yy use the number of seconds you want the phone to ring for in 5 second increments, max 30 seconds
dial *#61# call to confirm your ringer length
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There is a default time set by the carrier. GSM users may use the hash code provided above to change the amount of time in 5 second increments up to 30 seconds max.