You can get a Krown PocketComm TTY/VCO for $ 199.95. Basically, It's a "Type and Read" TTY or a "Speak and Read" VCO on the move. You can use it to connect to cell phones that are TTY compatiable. I'm just learning about this myself, so if you do get it, let me know how it is.
I myself use the sidekick 2, and its handy for everything. You can get e-mails, go on the internet, aol and yahoo messenger, get and send texts, take pictures (not bad quality either, every hearing person I know comments on its quality) and e-mail it on the move. I can't understand what the other person is saying on the phone however, so I use texting on my sidekick for when I'm mobile, and CapTel telephones which types down everything the person is saying to you live, and you can talk back.
There is also the 2 way CapTel telephone, which is where they install a second telephone line and in use with the CapTel you have, anybody who calls immediately can be captioned on the telephone and you can answer. (The 1 way CapTel requires callers to call the company first then you. Which can be a bit off putting for potential employers unfortunately.)
You can find out more about sidekick 2 on the t-mobile website. It is a cellphone that does everything. Since its up to your mum, I would probably push for the sidekick most of all. Right now, its a very trendy thing to have (popularized by Paris Hilton and most celebs right now). It would definitely help you gain your indepedence, and every person you will meet will pretty much be able to text you on your sidekick. Its questionable though whether you will be able to carry on an interview with a potential employer if you use phones solely for text messaging. Otherwise, if you can use it to actually communicate and know what the other person is saying, then props. Go for it.
I hope this and the other info helps. Good luck.