I think that Locke enjoys to have a purpose. This is whether he needs to save the Island or talk to someone on the phone or go on a walkabout.

I also think he over obsesses on his purposes (much like me while watching LOST) so when he loses his attachments he hurries to cling to another one.
Kate Segal does not really sound like Helen on the phone, though many people sound different on a phone.

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