Unless you have unlimited calling, extra minutes cost money. Checking usage from your cell phone is FREE.
Here is how is works for the Big Four Carriers:
AT&T – dial *646# and press “send”
T-Mobile – dial #646# and press “send”
Verizon – dial #646 and press “send”
Sprint – dial *4 and follow prompts
Most cell phones let you check your usage. Contact your carrier for details.
source: AARP – your money
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