The 128 GB tier of the iPhone Air on AT&T. Starting from $10.28/mo.

The 128 GB variant of the iPhone Air starts at $10.28/mo on AT&T via Installments over 36 months. Outright purchase pricing varies; see AT&T for the full quote.
128 GB is comfortable for most users — about 30,000 photos, ~50 high-quality apps with media, plus several hours of 4K video. Heavy ProRes / RAW shooters and offline-music collectors should consider 512 GB or higher; iPhone Air doesn't expand via SD card.
The 256 GB tier on AT&T typically runs a few dollars more per month than 128 GB on the same plan. Check the storage-tier table above for the live monthly delta.
No — iPhone Air doesn't support expandable storage, and Apple/Samsung don't offer post-purchase storage upgrades. Pick the tier that fits your two-year plan.
AT&T offers trade-in toward new iPhone Air purchases — credit varies by your old phone's condition and any active promo. Higher storage tiers typically receive proportionally larger credits.