On-line cell phone recharge
They typical approach when you are out of saldo in your cel phone is to go to the nearest pulpuria for a recarga. If, however, you are a regular Internet user, there are alternatives. They are generally billed as a way for your rich relatives in some other country to send you something but they work equally well for an in-country recarga.
While not the only company offering the service, Mobile Recharge is one that is well known. They do offer service for Claro and Movistar in Nicaragua along with lots of carriers in many other countries. Discount vary but seem to be pretty much what you would expect locally.
Nothing magic here but it could be a useful link when you run out of saldo in the middle of the night.