I think the only reason the 4th is involved is the employer is the government. A big stretch.
I don't agree with this rationale, as far as, it seems to presume that the government, as an employer, is using its influence, as the government, to get the records from the phone company for its phones. If the government is the employer, and it is reasonable to assume that civilian employers would have the same access to the texting/phone records of those communication devices the company owns and gives to its employees as the government does, then it wouldn't be as if the government was actually using any government pull to invade its employees' privacy. Now, if the phone company was unwilling to give those same records to a civilian employer that it would give to the government, as an employer, then I might say there is a case. Now all of this is assuming that the phone carrier is the same, otherwise, it wouldn't necessarily be the government's pull that was giving it access to the records, but the policies of the phone service company.
Now, I will say that I think any employer should be able to access the texting/phone records of communication devices that it lends out to its employees. The employer owns those phones and pays for them. To use the example given before that if it was your buddy's phone, well then the buddy most definitely should be able to access what was sent over his phone. I'm not sure what exactly the buddy could do to punish you for improper use of his phone, since he probably isn't employing you, but if you compare it to this case, it might be like suing him for telling your wife that you were using his phone to text your girlfriend.
And even if you assume that the employee is paying any overage charges, it doesn't mean that the overage, if there was any, was the only minutes that were used for personal purposes. And, from this case directly, it said that the guy only actually used the device 3 times while on duty to text for official purposes. So, that could be used to determine ways to buy the least expensive plan the employer actually needs. If official texting is only needed for a few times a month, per employee, then maybe the force could save money by paying per text, but they aren't going to know that without looking into the records.