This story from TMCNet is most interesting:

One source told Jackson [Vodafone] New Zealand had chosen one of two billing system options for the project, but Vodafone corporately decided subsequently to run with the other.

The core problem seems to have been one of scalability, Jackson says, "that as the business grew, the billing system wasn’t able to scale up… It’s understood the introduction of PXT was offered free for six months, simply because it couldn’t be billed."

"In December 2003, IBM was selected as the integrator for Vodafone's new CRM, billing and provisioning systems in New Zealand, Australia and Fiji. The CRM component was to be based on Siebel, which is used in several Vodafone country subsidiaries."