build a client app for MQTT protocol

good afternoon, we are looking for a developing company that have proven experience in developing apps to communicate with MQTT protocol (examples of apps will be requested). Apps to be developed for both iOS and Android platform. Details for quotation will be sent subsequently, I am currently shortlisting developers. please begin your bid with mqtt to make sure you have read the above. Please do not bid if you have never developed for this protocol. companies or teams of developer will be preferred.