Offer to 'pony up' yours-without question. Never, ever, date a woman on your job. This is called 'career suicide'. Don't give up your work number unless she is willing to do the same. If you do exchange numbers on the job, remember to not abuse the privilege and ask her to do the same.
Office gossip is still office gossip, regardless of who is making the calls.
It cuts down on you carrying emotional baggage. Her biological clock may be ticking, but yours should be on 'standby' until you have popped the question. That subject, even during our so-called 'enlightened' era spells disaster. You and she need your living space. Feedback from a friend can spare you a lot of future heartache.