the monthly fees for those are outrageous for occasional usage. $30 a month for tmobile + a one year commitment, $20 for at&t. if you're a constant business traveller it makes sense for airport connectivity, but for casual users? yikes!
tmobile looks the better deal for occasionally connecting. prepaid minutes at ¢10 per, with a minimum of 60 on first connection. at&t just does day passes.
if at&t were smart, they'd offer iphone users a deal. $5 a month extra for unlimited access to their wifi hotspots. it'd reduce the strain on the EDGE network (who knows we may get surprised still)