Since we have had some good discussion about cell phone plans and a lot of people do negotiate better plans for themselves, I thought it would be a good idea to put this information together. I will personally give my experiences with Rogers and let other people speak about their experiences with their carriers and try to summarize it here.
Rogers:
% discount range submitted by other forum users: 25-30%
Asking to cancel your phone, get it unlocked, or pay out your contract are good ways to get put to the "loyalty department" although you can usually get them by asking directly. Sometimes they do not like to forward you to the loyalty department, so you might have to "spice it up" a little with a bit of embellishment.
Now, there are 2 ways to get offered a deal once you are speaking to someone from the loyalty department:
1) Tell them you are planning on switching to another carrier or cancelling your contract. I personally throw in something about how I would prefer to stay with Rogers but they can't meet my needs currently. At this point they will usually offer you reasonable discounts on top of special plans to entice you to stay.
2) Bring to their attention what kind of features you are interested in creating a "customized" bundle/plan for yourself and start asking them how they can give you additional features (i.e. premium voice mail, more data, etc) and stay in your budget.
With either option it is important to do your research. Obviously it is good to know what the competition is offering, but most of the time that is actually pointless. You should focus on things such as "what features do I want, how much do they cost, what am I willing to pay, what deals are other people getting, what does it cost to go over your usage, etc." Focus on the fact that they need to offer you a package that meets your needs and budget and the cookie cutter plans on their website do NOT. One mistake some people make is to not know what current promotion plans the company is offering and get offered that plan. WE ARE NOT speaking to loyalty just to get offered a plan that is on their website already! Do not fall for this trick (I'm looking at Tellus and Bell... they tried to do this to me)!!
Remember the key point to any negotiation is to go in sounding like you have done your research and know what you want (and please be polite). Trying to get them to give you a ridiculously insane deal often looks like you have no clue what you're talking about (i.e. asking for 1GB data + unlimited talk and text for $25).
Bell: How to Negotiate With Retentions; Getting the Absolute Best Deal Telus: