forensic requirements for PDAs

Hello,

I was wondering about what requirements exist so that a PDA device would be considered as forensic sound acceptable. For example if an investigator uses a PDA to record some notes related to a case, what requirements should exist to make these notes acceptable in the court of law. These may be related to OS, model etc.
Also would it make any difference if it would be a smart phone or a PDA?
Still looking at their differences but some are quite similar.

Any help will be welcome.

Thanks.