Your last message said the phone was a red herring, and I completely agree with that.
My thoughts on your cell-phone questions (just thoughts, I don't know-for-sure any of this). These are my current understandings, if anyone else knows differently, please feel free to correct me:
Is it common for people to destroy their old cell phones after getting a new one?
Not for normal folks, no. Here's what usually happens:
-hand me down to other family member/friend
-sits around in junk drawer
-recycled at Best Buy
-garbaged
...whether or not the phone gets wiped before hand (simple factory-reset type of thing) is user-dependent.
Do cell phones really remember every text you ever sent?
Depends on the cell phone and the software it's running on.
Older ones - yes, until memory limitations are met
Newer ones - I don't think so, I believe they have built-in default time limits now (ie - only kept for a year or so, maybe a month... depends on software used)
Can you delete an old text message, or is it just removed from the list but remains in memory?
If you delete an old text message, it's deleted from your phone. Like putting a file into the recycling bin and then emptying the recycling bin on your PC.
Like your PC... there are some ways to recover deleted things that have varying results.
But, really, this doesn't matter at all.
Every message you send to/from your phone goes through
the phone company database as well.
When you delete a message from your phone, it definitely does not delete it from the phone company's database.
The phone company
never deletes their database.
That's why courts subpoena cell phone records (including text messages) from
the phone company and not from you and your phone directly.
In this sense, you are completely correct when you say that destroying Brady's cell was a red herring. If any text messages were required by police, they could (even now) still get them from Brady's phone company.
Does that text message history go away when you get a new cell phone, or does it transfer over like your contact list?
I do not believe it transfer's over like your contact list.
However, newer and newer phones and transferring-software may be correcting this and perhaps now such things are transferred over if you're going from iPhone 5 to iPhone 6 or Android phone to Android phone... these things would not be copied over if you're going cross-platform (contact list can sometimes still be transferred cross-platform, but I doubt text-history would at this point).
Given that Brady's cell phone could contain confidential financial and legal information, do lawyers perhaps always advise clients with significant net worths to destroy their old cell phones?
Sounds like a prudent procedure to include if you ask me.
Things like text-messaging, though, would still leave a copy with the phone company.
If you send text-messages through an app (say, like
Viber or
Snapchat or even
Twitter) your phone company does not have a record of such texts. However, those individual companies themselves would have their own never-deleted database of everything you send/receive that could be subpoena-ed by police and such.
Therefore, it's possible that police want to look at the phone to know what companies they should send subpoenas to.
If they don't find what they're looking for at the phone company, they may not know if Tom has an account with any other messaging app (probably hundreds of possibilities, but mainly in the 10-15 range of popular ones?)