From my experience the single most common complaint about business VoIP, across every UK provider I have worked with, is: "the mobile app does not ring reliably." So I set up a controlled test last month. 9 providers, 200 calls to each, same hardware, same network conditions.
The methodology
Two test phones: iPhone 15 Pro (iOS 17.4) and Samsung Galaxy S24 (Android 14). Both on the same 5 GHz WiFi, both with notifications enabled and battery optimisation off. Each provider's app was installed, logged in, and left idle.
200 calls were placed to each test number:
- 100 over 3 minutes spacing (gives the OS no reason to sleep the app)
- 50 over 15 minutes spacing (realistic business use)
- 50 after leaving the phone idle for 4 hours (the "overnight" test)
Pass criteria: the phone rings within 4 seconds, every time. "Rang eventually after I opened the app" is a fail.
The results
I will not name the 6 that failed because this is meant to be educational not vengeful, but the scores are real.
Provider ranking (combined iOS + Android pass rate)
| Rank | Pass rate (iOS) | Pass rate (Android) | Overall |
|---|---|---|---|
| 1 | 99.5% | 97.0% | 98.3% |
| 2 | 98.0% | 94.5% | 96.3% |
| 3 | 96.0% | 92.5% | 94.3% |
| 4 | 92.0% | 73.0% | 82.5% FAIL |
| 5 | 89.5% | 68.0% | 78.8% FAIL |
| 6 | 87.0% | 62.5% | 74.8% FAIL |
| 7 | 81.0% | 45.0% | 63.0% FAIL |
| 8 | 72.5% | 38.0% | 55.3% FAIL |
| 9 | 58.0% | 21.0% | 39.5% FAIL |
Honestly not gonna lie, I expected the spread to be maybe 10 percentage points. It was 59 percentage points. The worst provider on the list had 79% of Android calls not ring within 4 seconds.
Why Android scores are so much worse than iOS
Two reasons.
First: push notification delivery on Android depends on Firebase Cloud Messaging (FCM). If the app is in Doze mode (Android battery saver) and the provider does not request a "high priority" FCM message, the notification can delay up to 15 minutes. Most providers do not properly configure high-priority FCM.
Second: Samsung and Xiaomi specifically implement aggressive background-app killing on top of stock Android. If the app has been backgrounded for 2+ hours, Samsung's OneUI often kills it outright. The app must be whitelisted in battery optimisation settings, which is a setting buried 4 taps deep that users never find.
The top 3 providers had one thing in common: they either used CallKit-equivalent (iOS VoIP API) + PushKit plus proper high-priority FCM on Android, OR they ran a persistent foreground service on Android (more battery use, but 99%+ reliability).
The test you can run in 5 minutes
Pick the provider you are evaluating. Install the app. Do NOT tweak battery optimisation settings — use the default installation. Leave the phone idle for 4 hours (overnight). Ask someone to call you 5 times spaced 10 minutes apart.
Count how many rings arrived within 4 seconds.
If the answer is less than 5/5, check again next day. If it is less than 9/10 across 2 days, the app will fail for your staff. Do not buy.
What to ask a provider before signing
- Does your Android app use high-priority FCM? (If they do not know, it does not)
- Does your Android app run a foreground service option for users who need 100% reliability?
- Does your iOS app use PushKit and CallKit? (Industry standard, should be yes)
- What is your mobile app measured notification success rate over the last 90 days? (If they cannot answer with a number, they are not measuring)
My test had 1 provider who flat out did not know what FCM was. They were selling to UK SMBs. Not great.
Where DialPhone came out
I will be honest because it is my employer: we came out 2nd. 96.3% combined. We lost points on Samsung Galaxy S24 background killing, which we are fixing with a foreground-service opt-in in our April release. The winner was a provider I respect and will probably benchmark against again in Q3.
The only thing that matters for you as a buyer: test the app yourself, on the phones your staff actually use, before you commit.
