ESN standards, just like web standards
Worked for a company integrating Motorola's ESN into our main product. It's all meant to be based on an international standard, so Motorola could, in principle, be replaced by another provider. The reality, like web standards, is there is ambiguity in implementations of the standard which will make it impossible to change providers without a huge amount of development and testing.
The other part is that Motorola's functionality is incredibly flakey and unreliable, at least when I was working with it. There is no reason to believe it has improved.
AC for obvious reasons.