It probably appears as coming from the last number you configured because it is coming from that last number.
Which Voice Service a call goes out on depends on several factors:
1. The setting of PrimaryLine.
2. The Phone Port Digit Map.
3. The Phone Port OutboundCallRoute
4. Any **n that you have prepended to the number you dialled.
The short answer which you can use immediately is to dial **n at the start of a number where
n=1 to use Voice Service 1
n=2 to use Voice Service 2
n=3 to use Voice Service 3
n=4 to use Voice Service 4
An alternative which is a better but more difficult solution is to read, understand and implement what is contained in the tutorial
http://www.obihai.com/docs/OBi-DigitMapCallRoute-Tutorial-v1-1.pdf.
