A recent interview on Twisted Wire about prepaid phone companies has highlighted an area of some concern;

It seems that a standard practice in the pre-paid phone card market is for companies to produce multiple cards under different brands, which, when initially released to market use premium “high quality” routes for call connection, and then gradually begin to use cheaper, lower quality routes when the card is popular with customers.

Of course, this is akin to bait and switch tactics, but without a standard of communication quality, this underhanded tactic seems legal.