Data and Calls at Local Rates. A Companion App to the SIM Card

Drimsim is a mobile app for cost-efficient mobile service abroad. It runs on iOS and Android.

6 months for MVP development


10+ integrations with external services



To develop an app that allows using cellular services at attractive prices when traveling abroad, on tourist or business trips.

The app had to work in tandem with the original SIM cards of the customer.

Localization languages: Russian and English.



We have developed an app for iOS and Android.

The app provides a rate chart for each country. Users can track their expenses and view details on their tariffs.

The app incorporates VoIP calls. These use solely internet data traffic, which makes them a cheaper option to regular calls.

Great focus has been given to tech support. It is implemented via the Freshchat service.

Development Process

Business logic. The app works in tandem with Drimsim SIM cards, which can be ordered on the customer’s website. The company provides their services using other carriers’ networks around the world.

When the user arrives in a new country, the SIM card automatically switches to the local carrier’s rate, and its details are displayed in the app.

Our first task was to implement integration with the carrier to interact with SIM cards.

In-app voice calls. We have implemented VoIP calls inside the app. Any user can make a call and only pay for the data used.

Tech support. At first, we implemented our own chat based on push messages to save costs and maximize customization potential, but its stability was rather poor. On top of that, we found out after the release that people used tech support quite actively, for instance, to solve SIM cards registration issues or to figure out what they spent their data on. For this reason, we focused on developing robust tech support features.

We tried several solutions and settled on Freshchat for chat and F.A.Q. implementation. We chose it for its stability and configuration flexibility.

Admin panel. It displays usernames, orders, logs for each ticket, transaction history, user phone numbers, and so on. We created it to keep track of all tickets and responses, and implemented the ability to manually add data when an external service sends an invalid response. This was helpful for developers during tests, and now it helps the tech support team to troubleshoot user issues.

Integrations with external services:

  • Carrier: to interact with SIM cards.
  • Bringo and B2CPL: to deliver SIM cards ordered by users in the app or on the website.
  • Voximplant: for VoIP.
  • Stripe and CloudPayments: for acquiring.
  • Freshchat: for the tech support chat and F.A.Q.
  • Branch: for the referral system.
  • Mailchimp: for email newsletters.
  • GCM: for in-app notifications.

The Hardest Part

Getting the carrier integration up and running. The carrier’s backend was unstable, and occasionally the server sent responses with missing information. We realized that we needed a different approach to fetching data to ensure that it’s always complete, the app works consistently, and the tech support can help users.

How we solved these tasks

We built an admin panel that allowed editing data coming from the customer’s backend. As a result, at first the app outputted all necessary info on our side, and afterwards consistent data started coming from the carrier’s side as well.

Technology Stack



The app works in tandem with the customer’s special SIM cards. The user can check the app to see the rate applied to the SIM card in the country of visit. Furthermore, the app shows the money, minutes, and data spent.

In-app calls can be made with VoIP. The call itself is free, and the user only pays for the data consumed.

In case of any issues the users can contact tech support in the app.


For the calls made in the app, the user only spends their data. This comes out cheaper than regular calls.

In-app VoIP calls

For the calls made in the app, the user only spends their data. This comes out cheaper than regular calls.


Let’s discuss your project!

It is free. We will tell you how the application will solve your problems.

Similar projects





White sphere