Fewer repeat calls.
Check incoming lists against existing leads and duplicates in the same file, so you don’t waste time contacting the same company again.
Cold calling with a clear next step
No duplicate leads. No missed follow-ups.
Bring order to your cold calls: clean up contact lists, make your calls, and schedule callbacks and appointments with reminders. No complicated CRM required.
No account · Lead data stays on your device · Try for free
See how Callstack worksNew in 1.3.0: scheduling, calendar & reminders
Calling session: Open
Example Company LtdAlex Example
Call
Note
Discussed the proposal. Agree on the next step.
CallbackAppointmentCustomer
Keep follow-ups in sightCallback · Example Company Ltd10:30-10:45 · Scheduled
Feature illustration · not an app screenshot
START WITH THE LISTS YOU ALREADY HAVE
More contacts shouldn’t mean more loose ends.
Whether you work in Google Sheets, Excel or a CRM, combining lists can bring in the same company twice. Callbacks get buried in colour-coded cells and notes. Callstack turns them into clear next steps.
Follow-ups become tasks.
Turn “call back later” into a scheduled callback. See what’s coming up and spot overdue contacts at a glance.
START WITH A CLEANER LIST
Clean up your lead lists before you call.
Keep using the contacts you already have. Export them as CSV or Excel files and import them into Callstack.
- Let Callstack suggest column mappings, then check them before importing.
- Filter out duplicate phone numbers after phone-number normalisation.
- Identify similar companies when their location matches and their names are sufficiently alike.
- Bring in contacts, locations and notes; use an alternative phone column as a fallback.
Checks cover your existing leads and the incoming file. Imports never overwrite existing leads. No duplicate-detection system can catch every duplicate.
Contact list ABraun Henning MalerfachbetriebOchtendung
Contact list BMalermeister Braun HenningOchtendung
Identified as a duplicate
Example: matching location and a strong company-name match. Only one entry is imported.
Choose file → Check columns → Preview → Import
Feature illustration · not an app screenshotGIVE EVERY CALL A NEXT STEP
Plan your follow-ups. Keep them on your radar.
A contact asks you to call back? Choose a date and duration. Callstack shows available start times and checks for scheduling conflicts again before saving.
- Available times within your working hours, with your chosen buffer.
- Checks against Callstack appointments and callbacks, plus your device calendar if you allow access.
- Chronological lists with today, tomorrow and clearly marked overdue tasks.
- Record the outcome after a call, reschedule or update the status.
Duration: 15 minutes
- Callback
- Appointment
- Device calendar
Your week, at a glance.
The read-only week view shows callbacks, appointments and, with permission, device calendar events. Tap an entry for details. Callstack never creates or changes events in your device calendar.
Reminders that follow your schedule.
Callbacks: 5 minutes before. Appointments: 15 minutes before. A daily overview is scheduled 10 minutes before your chosen working-day start.
Notifications require your permission. Your operating system, focus mode and battery settings can affect delivery. Locally scheduled reminders are refreshed when you open the app.
KEEP COLD CALLING SIMPLE
One lead at a time. One clear next step.
- 1
Make the call
Open a lead or start a calling session in Open or No answer. Callstack opens your device’s phone app.
- 2
Capture the outcome
Add a note and choose a status. For No answer, you can see when the last call was attempted.
- 3
Move things forward
Schedule a callback or appointment straight away. In a session, move on to the next card without navigating a full CRM.
A clear place for every contact.
- Open
- No answer
- Callback
- Not interested
- Appointment
- Customer
Search your leads, access saved data offline and export it as CSV or Excel. Callstack is not an automatic dialler and does not record calls.
YOUR CONTACTS STAY WITH YOU
Stored locally. No Callstack account.
Callstack processes lead and calendar data on your device. That data is not uploaded to our servers. Device calendar access is optional and read-only; local Callstack scheduling works without it.
App stores and RevenueCat separately process the data needed for purchases and subscriptions. Backups and exports are shared only when you choose to share them.
How Callstack handles your dataSTART FOR FREE
Try it with your real workflow.
15 processed leads
The one-time trial counts processed leads, not imported rows. A lead counts on its first later status change, and only once.
Choosing a status when creating a lead does not count. The allowance does not renew each month.
Keep working without limits
Choose a monthly or annual subscription for unlimited processing while your subscription is active. After the trial, Pro also unlocks new leads, imports, deletion and JSON backups.
Your existing leads remain available to view, search and export. See current prices and available offers in the app and your app store before purchasing.
What is Callstack?
Callstack is a mobile app for cold calling and follow-up management. Import contact lists, check for duplicates, call leads and schedule callbacks and appointments. It is designed for salespeople and self-employed professionals who want a focused alternative to a full CRM.
Can I use contacts from Google Sheets, Excel or my CRM?
Yes, by exporting a file. Callstack imports CSV, XLS and XLSX files. There is no direct Google Sheets sync or general CRM integration. Company name and phone number are required mappings; contact person, alternative phone number, location and notes are optional.
How does Callstack detect duplicate leads?
Matching normalised phone numbers always count as duplicates. For different numbers, both leads must have the same normalised location and sufficiently similar company names: at least two strong shared name tokens and at least 80 percent token similarity. Legal suffixes and generic trade terms are not strong identifiers. Checks cover existing leads and the incoming file. Existing leads are not overwritten, and not every duplicate can be guaranteed to be detected.
How do I schedule callbacks and appointments?
When choosing the relevant status, select a duration, date and available start time. Callstack accounts for your working hours, buffer and existing callbacks and appointments, then checks again before saving. Timed device calendar events can be included if you allow access. All-day events are shown for reference but do not block times.
Does Callstack sync with my calendar?
No. With permission, Callstack reads your device calendar for conflict checks and the read-only week view. It never creates, edits or deletes device calendar events. Local scheduling still works without calendar access.
What reminders are available?
Local callback reminders are scheduled 5 minutes before the call and appointment reminders 15 minutes before. A daily overview with separate counts is scheduled 10 minutes before your working-day start when tasks are present. Permissions, focus mode and battery saving can affect delivery. The limited forward schedule is refreshed when you use the app; delivery cannot be guaranteed indefinitely without reopening it.
Does my data stay on my device, and can I work offline?
Lead and calendar data is processed locally on your device and is not uploaded to our servers. No Callstack account is needed. Saved leads and notes are available offline. Calls use your phone app; purchases, subscription checks and updates may require a connection. App stores and RevenueCat separately process the necessary purchase and subscription data.
What does Callstack cost, and what counts as a processed lead?
Callstack is free to install. Your first 15 distinct processed leads are free once: a lead counts on its first later status change after creation, and only once. Importing alone and choosing a status at creation do not count. During the trial, imports have no row-based trial limit. After the trial, further processing, including new leads, imports, deletion and JSON backup/restore, requires an active monthly or annual subscription. Viewing, searching and CSV/Excel export remain available. The app displays current store prices and eligible offers before purchase. The free allowance does not renew monthly.