Retrieving deleted sms's from custodians mobile phone

Have anyone considered a subpoena of the carrier to provide the data?

I am unconvinced carriers do not have at least a 'short period' storage of SMS messages.

I say this because some phones cannot accept, for example, MMS messages. To fix that problem carriers send a standard SMS to the non-compatible system and store the MMS, accessible online by the recipient.

This action occurs in UK if

a) statutory provisions prevent operator from automatic disclosure failure/unable to respond to SPOC request;
b) operator is uncooperative to meet conditions of licence;
c) regular occurrence where defence seek data