Just got a new nexus5 from google, I want to upgrade my phone via self serve, do I even need to do that? If I enter my existing sim card and it just tells me that it is "in use" and that I need to enter a new one. Sometimes I find the self serve section is very unintuitive, like MS Office...
You don't need to update your phone. But if your new phone uses a different size SIm card, you need to update your Sim info through self serve.
Go to Self serve > Mobile Phone > Swap Mobile Phone
Step 1 : "Upgrade my current phone"
Step 2 : "Does the new phone you're upgrading to use a SIM card?"
Select "yes", and enter a new sim # then continue