Does anyone know if it is possible to use MQTT in iOS development like in Android? Is there a library or something?
Try this. It's much better than mosquitto: The Paho project provides open-source client implementations of open and standard messaging protocols aimed at new, existing, and emerging applications for Machine‑to‑Machine (M2M) and Internet of Things (IoT). The Paho MQTT C Client is a fully fledged MQTT client written in ANSI standard C. It avoids C++ in order to be as portable as possible. A C++ layer over this library is also available in Paho. In fact there are two C APIs. "Synchronous" and "asynchronous" for which the API calls start with MQTTClient and MQTTAsync respectively.
C - http://git.eclipse.org/c/paho/org.eclipse.paho.mqtt.c.git Wrapper - https://github.com/relayr/apple-mqtt-example