I am going to assume by "mobile phones" you mean the 7921G or 7925G. Speed dials are a feature of that model and a referenced in the phone's documentation, not UCM. Cisco UCM has no feature called speed dials which is why you cannot find documentation on it. The closest that UCM comes is the speed dial line button type. The UCM-level features that are equivalent are :

1. Abbreviated dialing. You press a one- or two-digit index number representing the number you want to dial and then the AbbrDial soft key. This is a per-device setting (i.e. not global). These are configured by the user on the device using /ccmuser or the adminstrator by assigning a Speed Dial line button type to a device. If assigned to a free button it will act as a one-button speed dial. If you associate it beyond the available buttons, the index number shown to the left becomes its Abbreviated Dialing index.
   
2. Fast dials. These are Personal Address Book entries that you have configured as a fast dial through /ccmuser. They are accessed and dialed through the Personal Address Book service. These are per-user settings.
   
3. Translation patterns. Many other PBX systems have an explicit concept called Speed Dials that are globally available to all users. UCM doesn't bother with that feature because Translation Patterns can do that instead. Cisco just doesn't point this out very well. You can create a translation pattern that translates FROM anything TO anything. For example: *411 translates to +16085532447.