Welcome to the stone age
It never ceases to amaze me how backwards the USA are when it comes to mobile telephony. No competition betwen networks (meaning that users get royally shafted at avery corner) and you even have to pay to receive calls!
This non-removable SIM deal would not be allowed to happen here in the EU (I'm in the UK). One of the reasons for this being the mobile phone manufacturers who do sell reasonable numbers of SIM-free phones that are not tied to any network in particular. Not to mention the operators themselves that offer more and more SIM-only contracts, thus avoiding having to subsidise a new phone.
I know I certainly would be unhappy if my operator tried to pull something like that off because I *NEVER* source my phones from the networks. Firstly, there's the SIMlock issue that others have mentioned. Then there's also the branding issue, which means that you can't update your phone's firmware until the operator that branded it decides to pull its finger out and approve the update. For example, I have, among other phones, a Nokia N73 that was originally a phone supplied by 3UK. The latest, operator-approved firmware version is the FIRST one ever that the phone was released with. In other words, 3UK have approved ZERO updates since the phone was first launched on the market in 2006(?). Thankfully, the phone has since been debranded and is now running up-to-date generic Nokia software.
Since then I've had an N95 (from T-Mobile but since debranded), a completely generic and unbranded N96 sent to me directly from the Nokia flagship store in Helsinki, and an equally unbranded and generic 5800 XpressMusic that I got from Nokia Retail in Manchester.
There's no way I'd go back to operator-provided phones now and I'm sure I'm not the only person like that.