We are required to tot up the number of minutes used for business calls and are reimbursed ratably for the same. E.g. on a 1,000 minute plan I use 750 for business calls. Company would cover 75% of my bill.
As a practical matter, it's a pain in the arse to check through a couple of dozen pages of calls so I just pay the bill myself.
In my previous job, I received a flat monthly cell phone subsidy which covered 90% or so of the bill.