@Dennis

From experience and after several years of practice whenever I encounter new networks and try to dial-up,  the:

 *99***1# 

Is the GPRS standard AT dialing that chooses a specific APN, in this case, the first APN on your phone...as per the order of APN list when you run 'Query Modem" on your "Control Panel > Phone and Modem Options"

*99***3#

Is dialing the 3rd APN etc etc

[there are not 4 stars, check on google always when in doubt ]


When you do *99# - this puts a wildcard and if set, it will usually result to the default subscribed APN for that network.
Usually the dialing computer will try all the APNs on ur phone/modem until it hits the right one.

w/r

Snn