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Many people with Spanish SIMs may notice sudden bursts of strange calls from unknown numbers. These can be confusing, sometimes hundreds of calls a day and it’s natural to worry about scams or personal harassment.
Here’s what you need to know.
What these calls really are:
Most of these calls are automated VoIP robocalls, generated by computer systems rather than humans.
They often make silent calls, where nobody speaks if you answer.
Numbers can rotate rapidly, with hundreds of variations all sharing the same prefix.
The system is simply testing whether numbers are active, this is called number verification.
Your number may be targeted if it has historical public exposure, such as appearing online in the past on websites, forms, or work contact lists. Older numbers are particularly likely to be affected.
These calls are automated number testing calls. Their purpose is t check which phone numbers are active and answered by a real person. Numbers confirmed as live are then sold on as active call lists to marketing companies or scammers.
How to recognise robocall patterns
The best way to identify these calls is to look for patterns:
Unusual prefixes
Calls often come from the same area prefixes repeatedly (e.g., numbers starting with the same 5–6 digits).
High-volume repeated calls
Hundreds of calls may arrive in bursts.
Each number may be slightly different, but the prefix is the same.
Silent or empty calls
If you answer, there is no one on the line.
Legitimate calls (hospitals, insurance, or official contacts) will always have a human or automated voice.
Tip: A quick glance at the first few digits (prefix) can immediately tell you whether it’s likely a robocall.
What you should do:
Do not answer numbers matching these robocall patterns.
Silence and non-engagement prevent your number from being marked “live.”
Answer unknown numbers if you suspect they could be legitimate.
Examples: hospitals, insurance companies, banks, or other important contacts.
Do not block unknown numbers if you need to receive legitimate calls.
Blocking is ineffective against rotating numbers and may prevent real calls from coming through.
Ignore voicemails from unknown or silent numbers
Legitimate contacts usually leave a message identifying themselves.
Recognise that this is automated, not personal.
Your number is part of a global automated testing system.
The system will eventually mark unresponsive numbers as low-value, and call frequency will decrease.
Roaming vs local SIMs
Robocall patterns can affect any number, whether the SIM is being used locally or while roaming.
Roaming may make calls more noticeable because network-level filtering is weaker abroad, but numbers are targeted globally.
Advice on receiving calls:
Check if your mobile phone has a setting for wifi calls which you can disable. After disabling, restart your phone.
Look at the prefix: repeated unusual prefixes are a key sign.
Repeated numbers: hundreds of variations, same prefix, usually silent.
Safe approach: do not answer robocall patterns, only answer numbers that could be legitimate.
Do not block unknown numbers if you need to receive important calls.
Reassurance: these calls are automated, not personal, and will reduce over time.
By understanding these patterns, you can protect yourself from stress, avoid accidental engagement, and still receive important calls when needed.
