We actually switched to a Primus long distance plan a long time ago, originally we were on the plan that was capped at a maximum charge of $20.00 (well plus the usual fees permitted by the CRTC). When I called them for service at one point, the service rep apparently switched me to this new flat fee plan, insisting that the old one was not available any more (so much for supporting legacy plans in order to keep customers).
Everything worked fine for a long time, and it's nice to have a fixed cost so you know in advance how much you are going to be paying for your phone bill.
The problems only started when I decided to leave this phone plan. Apparently Primus had introduced a 30 day notice policy for cancellations some time during the term of my contract and missed informing me of the change of terms. So when I switched long distance providers (and home phone providers, too), I thought placing my order with the new provider would be sufficient until I received another invoice from Primus
No problem, I just called Primus and asked them to credit the bill. The service agent then told me that the bill would not be automatically charged to my credit card and everything should be fine. Of course when I checked my credit card statement, I still saw a charge there from Primus. So I call again and ask them for a refund. They say I should be initiating a back charge via my credit card company instead and that would be a much quicker way to deal with it. So I check with my credit card company then they confirm my suspicion that a back charge also takes a bit of time, and normally they prefer the merchant just to issue a credit.
So I figured, let's do Primus a favour and call them again so they can issue a credit without it costing them any additional funds. Well, no such luck. This time they actually tell me, that I should not be getting a refund, since I did not give 30 day notice, as per the contract. And they stick with that opinion until I finally involve the Better Business Bureau and the matter gets escalated to their "Executive Response Team". This team in the end canceled the charges to my account and agreed to a back charge from my credit card company - but what a hassle to go through for $25.
So I guess the lesson here is to make sure to be aware of changed terms and conditions for your contracts and give enough advance notice. And for someone not planning on canceling their contract, Primus might still be a good choice for long distance service ;-)