How much extra would it cost to add a line to verison wireless?

my grandmaw pays 50$ a month for 1 phone with unlimeted texting and calling. how much would it be for 2 phones unlimeted texting and calling?|||Your grandmother cannot have unlimited anything for $50/month. The least expensive calling plan is $40/month and that's just 450 minutes. Unlimited calling is $70/month. Unlimited texting is $20/month. Her bill would have to be $90 plus taxes and fees for unlimited voice and texting for 1 line. Unlimited talk and text for 2 lines is $150/month plus taxes and fees.|||it would be $10 extra per phone per month