Meaningful disclosure is the issue here. The collector blocking their number, or listing it as unavailable, is not a violation but the collectors do need to inform the consumer that the call is from a debt collector. In Knoll v IntellRisk, the court said:No court has addressed whether § 1692d(6) applies to caller identification devices. Noting that § 1692d(6) applies when a debt collector places a call, Knoll argues that a debt collector must meaningfully disclose itself on a caller identification device. Defendants refute this argument on several grounds. First, they maintain that Knoll’s position is impracticable because the text available on a caller identification device is insufficient to make a full “meaningful disclosure” under § 1692d(6). This argument is baseless. To meet the “meaningful disclosure” requirement, the caller identification device need only display that the call is from a debt collector.http://www.jenner.com/files/tbl_s69NewsDocumentOrder/FileUpload500/1541/Knoll%20_v_IntelliRisk_Management_Corporation.pdf
If the collector leaves its name where the consumer can reasonably connect that name with the collector being a collector, then there is meaningful disclosure. No name, no number is not meaningful disclosure.
The problem with no name, no number is that the consumer is unlikely to pin that call on a collector without the collector admitting they did make the call via leaving a voice message. Then, if the collector identifies themselves in that message as a debt collector, there is meaningful disclosure.
Probably the best call to apply a meaningful disclosure violation to would be one with the collector's number, no name, and no message.
As silverzgirl says, don't go into court with this one violation. Use it with a bunch of others to show willful noncompliance.