On the other side, usually you don't own the software but only a license that grants you permission to use it.
Shrink-wrap licenses attempt to end-run this by making the product unusable unless the user agrees to forfeit his existing property rights. The legality of these sorts of after-the-fact licenses on a traditional retail purchase is very unclear.
It's for this reason that many do not object to cracking or modifying software which they have purchased. Indeed, there's no definitive argument that one shouldn't.
unless, of course you signed an agreement to not do that, in exchange for a cheaper price on the phone and some period of contract with a particular carrier...
yes you can - as long as you didn't have a prior agreement to not do it. For example, you downloaded a piece of software off a torrent site. you didn't have any prior agreement with anyone about anything. The agreement between the uploader who originally first distributed the software and the copyright holder is the only place that is valid in my view.