For native mobile apps, check out AWS mobile farmcheck out AWS mobile farm. They have a free tier of 250 minutes per month. They allow you to "rent" a device for some time: https://aws.amazon.com/device-farm/.
For mobile web, you can use developer tools in the browsers to set the agent string to your target device. Here is a tutorial: http://www.howtogeek.com/113439/how-to-change-your-browsers-user-agent-without-installing-any-extensions/Here is a tutorial.
Also, you can test the mobile web through the devices you "rent" from Amazon.