Whether or not you need to pay the $249 install fee (and have a tech visit) and be able to use your own D3 modem seems to depend on the area: »$250 fee to upgrade to 105 from 50?
Also, some Extreme 50 subscribers in the Northeast were recently automatically upgraded to Extreme 105 service (and Extreme 50 became the new Blast! tier).
Then there have been other posters who have had fun trying to upgrade to 105:
»Venting...Upgraded to 105, Getting Screwed..
»[Speed] 105 upgrade fun...NOT