Can I swap a htc one s sim card with an iphone 4 sim card?

My mom has an iphone 4 and I have a htc one s and we want to switch phones

The sim cards are the same size and fit in the phones but i cant text my mom with the iphone+htc sim card and she cant text me with the htc phone+iphone sim card

Does this mean it wont work?

Hi

yes you can use your iPhone card with HTC Sim
and your Mom use your HTC With iPhone Sim card
but you need to first unlock Both mobiles
you can unlock htc phone by enter unlock code, you can get unlock code from online unlock code provider
they will provide you unlock code with in a few hours(you can also ask for iPhone imei unlock in APPLE database from htcunlockingcode.com)
you can unlock your Mom iPhone by submit your IMEI in apple Database.
you can submit your iPhone IMEI by online iPhone Factory unlock service provider
I know some unlock code provider they will help you a lot