Skype for Windows Mobile is currently available in two versions:
It's one of the more heavily downloaded Skype tools.
Considerations
Memory: at least 12MBs of free storage is required.
Requires a high speed wireless connection, either WiFi or 3G.
3G wireless connections will incur data transmission costs.
It is essential to always use the latest versions available to avoid issues.
Mobile VoIP
is clearly the next big thing and it is surprising that Skype did not get onto it at an earlier stage. In the meantime the opportunity has been identified by third parties including Fring.
Fring works on all Symbian 8 and 9 devices, as well as Windows Mobile 5 and 6 devices including PDAs. It's an interesting option because it supports access not only to Skype, but also: MSN Messenger, Google Talk, ICQ, SIP, Twitter, Yahoo and AIM.
To catch up, Skype will need to plough a lot more effort into developing Skype tools for the mobile market.