Sprint said pre-orders were up nearly four times, compared to last year. Pre-orders also rose nearly four times at T-Mobile, compared with its next most popular iPhone.
However, the companies did not disclose specific sales numbers. Pre-orders started on Friday.
Details about sales of the new iPhone are scarce after Apple announced last week it would not release weekend sales data, saying the number was more a reflection of supply than demand.
"While the iPhone 7 update is more revolutionary than evolutionary, we believe investors could consider these strong early pre-order indications as being reflective of the impact of Apple's significant iPhone installed base expansion over the past few years," Stifel analyst Aaron Rakers said in a note.
Apple's shares were up 2.8 percent at $108.19 in morning trading. Up to Monday's close, they had fallen 2.1 percent since the iPhone 7 was launched on Wednesday.