Do you know the UTL, MTN anomaly?

SIR—Are you aware that it is more expensive to call MTN from an MTN phone than from a UTL landphone? According to the new rates of both telephone companies, from 7.00 pm to 9.00 pm, it is cheaper by sh110 per minute, for an MTN pay-as-you-go customer to call a fellow MTN customer using a UTL landphone. And on week days from 6.00 am to 7.00 am, 8.00 am to 7.00 pm and on Saturdays from 6.00 am to 7.00 am, UTL is cheaper by sh30 per minute. Can MTN explain this discrepancy? I thought it would be good to keep business within the network family by making inter-network calls cheaper than calls across networks. Fr Deogratias Ekisa Mbale