、？
Hey, wanna swap phone numbers sometime?
Literal
Ah, next time cell-number exchange do-not-[invitation-ませんか]?
A classic 'can I get your number' line. ケー番 is the colloquial shortening of ケータイ番号 ('cell phone number'). Note the interrogative negative ~ませんか, which is the standard polite invitation form: literally 'won't you exchange?' but functionally 'shall we exchange?'. 今度 is the slightly vague 'next time' / 'sometime soon', not a specific future moment.