A friend of mine has a mobile phone on GiffGaff and reckons that sometimes she doesn't receive texts that have been sent to her or indeed calls.

Putting aside the fact that in the case of calls it could sometimes be due to lack of signal, I wondered if GiffGaff's calls are given less priority somehow as their service is so cheap?

I've read that mobile phone companies can reduce call quality to increase the number of calls that can be made simultaneously via a single mast so it seems logical that they could effectively kick off GiffGaff users and give priority to traffic from the the "real" customers (of O2 I think)who are paying more?