I'd like to see data on past voice calls using an iPhone.
How far back can you check for a time duration that was made on my behalf without resorting to contacting a cellular carrier or looking at my past billing statements?
Within the UI (user interface) itself you can only view the history of the past 100 calls, irrespective of whether those calls were all made within the past day or past month etc. However, this is an inconvenient way to view your call history if it's something you want to analyse, especially if it's on a regular basis.
For something a lot more convenient, such as viewing your call history in a spreadsheet or text file, you can use 3rd party software such as iExplorer.
With iExplorer you can access, view and export this data, either directly from your iPhone or from an iTunes backup of your iPhone. This is important because:
If you're interested, you can read How to Export Your iPhone Call History.