Directly within T-Mobile? I don't think it's possible.
You can always download your usage records and use something like VLOOKUP in Excel or Google Sheets to translate phone numbers to friendly names.
That would be cool to change up the names, but that's not something we have available. My want to look at smplyunprdctble's suggestions. Smply's always got some interesting workarounds. (So organized!!! )
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