What type of apps do you want to build? I mean what's your business model, which factors does it include (your target customers, devices/platforms for it, high practical functionality etc.)? I ask because all these things are important while choosing the software development company and have a great influence on your general app's costs.Also in general while choosing such company it's necessary to make sure that the company has a proper post software development support system and is mobile for all current innovations in this sphere, and isn't too cheap, too cheap ones usually provide a low-quality work in this sphere. It's good to find a company with the same size as yours too because it'll make your general partnership more effective, it's a useful business strategy. Assess the costs involved and whether you can afford it, check if software consultancy gives a free detailed quote based on the best spec you have and always reviews from its previous clients.For example, as the good ones in this sphere are considered Apriorit, Innovecs www.innovecs.com/industries/telecom/ , Intersorg, XSolve, Radixweb radixweb.com/ , Netguru and Orases.