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, reports Reuters.
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.
Rival carriers AT&T Inc and Verizon Communications Inc were not immediately available for comment.
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.