diff --git a/src/Socket/messages-recv.ts b/src/Socket/messages-recv.ts
index a67d9dba..7eed7789 100644
--- a/src/Socket/messages-recv.ts
+++ b/src/Socket/messages-recv.ts
@@ -1603,12 +1603,21 @@ export const makeMessagesRecvSocket = (config: SocketConfig) => {
 	/**
 	 * Sanitizes caller phone number to fix known decoder bugs
 	 *
-	 * Issue: Brazilian landline numbers (12 digits) incorrectly get a trailing zero
-	 * Example: 551738025555 → 5517380255550 (off-by-one error)
+	 * Brazilian Phone Format:
+	 * - Mobile: 55 + DD + 9XXXXXXXX (13 digits total)
+	 *   Example: 5515991000000 (55 + 15 + 991000000)
+	 * - Landline: 55 + DD + XXXXXXXX (12 digits total)
+	 *   Example: 551541410000 (55 + 15 + 41410000)
 	 *
-	 * This helper removes the trailing zero if:
-	 * - Number is 13 digits (incorrect length)
-	 * - Starts with '55' (Brazil country code)
+	 * Decoder Bug: Landlines incorrectly get trailing zero
+	 * Example: 551738025555 → 5517380255550 (should be 12, not 13)
+	 *
+	 * Detection Logic:
+	 * - Extract first digit after DDD (position 4 in string)
+	 * - If digit is 2-5: It's a LANDLINE
+	 *   → 13 digits is ERROR → Remove trailing zero
+	 * - If digit is 6-9: It's a MOBILE
+	 *   → 13 digits is CORRECT → Don't touch!
 	 *
 	 * @param pn - Raw phone number from caller_pn attribute
 	 * @returns Sanitized phone number
@@ -1618,15 +1627,41 @@ export const makeMessagesRecvSocket = (config: SocketConfig) => {
 			return undefined
 		}
 
-		// Fix Brazilian landline off-by-one bug
-		// Remove trailing zero if 13 digits and starts with Brazil code
-		if (pn.length === 13 && pn.startsWith('55')) {
-			const sanitized = pn.slice(0, -1)
-			logger.debug(
-				{ original: pn, sanitized },
-				'Call: Sanitized Brazilian landline number (removed trailing zero)'
-			)
-			return sanitized
+		// Only process Brazilian numbers (country code 55)
+		if (!pn.startsWith('55')) {
+			return pn
+		}
+
+		// Check if it's a 13-digit number (potential landline bug)
+		if (pn.length === 13) {
+			// Extract first digit after DDD (position 4)
+			// Format: 55 DD X...
+			//         01 23 4...
+			const firstDigitAfterDDD = pn.charAt(4)
+
+			// Landline: first digit is 2-5
+			// If 13 digits, it's an error (should be 12) - remove trailing zero
+			if (['2', '3', '4', '5'].includes(firstDigitAfterDDD)) {
+				// Extra validation: only sanitize if ends with 0 (the bug pattern)
+				if (pn.endsWith('0')) {
+					const sanitized = pn.slice(0, -1)
+					logger.debug(
+						{ original: pn, sanitized, firstDigit: firstDigitAfterDDD, type: 'landline' },
+						'Call: Sanitized Brazilian landline number (removed trailing zero)'
+					)
+					return sanitized
+				}
+			}
+
+			// Mobile: first digit is 6-9
+			// 13 digits is CORRECT for mobile - don't sanitize!
+			if (['6', '7', '8', '9'].includes(firstDigitAfterDDD)) {
+				logger.trace(
+					{ pn, firstDigit: firstDigitAfterDDD, type: 'mobile' },
+					'Call: Valid Brazilian mobile number (13 digits correct, not sanitizing)'
+				)
+				return pn
+			}
 		}
 
 		return pn