I always felt configurations at the IN were as follows while testing your prepaid cards in other networks.
SCP: CAMEL phase and VLR address
SDP: Rates and profile
HLR: CAMEL phase
VLR : CAMEL Phase
The camel phase in all 3 nodes had to be equal or back compatible.
I also felt that there was no way of restricting usage on the VLR. As the VLR wouldn’t be able to identify if the inroamer is prepaid or postpaid and before you have a CAMEL tie-up you need to first have a postpaid( GSM ) launch. In other words, your postpaid customers should be able to roam first. So, if a network is open for postpaid subscribers, it is by default it is open for prepaid guys.
The restriction has to be done at your HLR. So, if they opened a particular VLR, they would allow every prepaid guy to make usage in the network that VLR supports.
Today, I learnt that you can create a separate profile for only those test IMSIs and allow only them to roam on another network.
You might wonder why this concept isn’t used for HNIs and why you need a hub like Roamware to determine preference settings when your HLR can so perfectly restrict usage to a particular network.
The HLR can restrict not determine 1st and 2nd preference.