Overview
If you want a working messenger on WM6.1 today, look into third-party XMPP clients (like Palringo, which also has a defunct server) or use it as a feature phone. But for the sake of completing your search query, let’s proceed.
While .cab (cabinet) files were historically used to install software on these devices, WhatsApp no longer allows these older versions to connect to its servers. The Status of WhatsApp on Windows Mobile 6.1
| App | Status | How to get CAB | |------|--------|----------------| | IM+ | Partially works (ICQ/Jabber) | Archived version on FreewarePPC | | Nimbuzz | Servers dead | Do not bother | | Fring | Servers dead | Do not bother | | SMS/MMS | Fully works | Built-in | | Email (IMAP/POP3) | Fully works (Gmail, Outlook) | Built-in – Best bet |