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Before you begin any of this, you need to know the DOFD and SOL on these accounts. Cell phone accounts have an SOL of two years. Lines of credit SOL vary by state, which you can google for yours.
1. Sprint or Nextel, it should show up as three separate accounts. Regardless of whether you had Sprint or not, since the company merged with Sprint and took its name, that's what will show up on your reports, the current name of the company. I had a loan with MBNA years before it was swallowed up by Bank of America, but on my report now it lists as Bank of America. Now, is this account current or derogatory. If it's current, and showing up as three current accounts, you may be better off letting it be wrong. If it's derogatory, dispute all three listings with the credit bureaus as duplicate accounts.
2. Every new CA that purchases the account gets to list on your report if it so chooses, but the old CAs have to delete their listings. You should DV the CA that's currently reporting after the SOL expires. If it's legit and you want to take care of it permanently, you can offer to do a PFD with the cuurent CA. If Cingular is reporting you can try to GW, same thing for Sprint if it's derogatory.
3. Follow the same advice as 2.
If you haven't already, read through these threads for more info on credit rebuilding and the forums.
Credit Scoring 101 Common Abbreviations Where Do I Start? State Resources
