This Question is based on below requirements.
1 - our application will need to use functionalities of Google Maps API like custom marker/Info pop up/Routing etc.
2 - our application wants to use Openstreetmaps or our ownmaps as the base layer.
Now , can we use Google maps API for functionalities and Openstreet map as base layer,so that I am not charged for using google data ? do they specifically charge for API usage ? isnt the 2500 request limit for http requests to google image/map server ?