my experience has shown that the following is common; for MMS/SMS to & from the following carriers, the delays are:

tmobile = 5-30 minutes
verizon = instantaneous (relatively)
att = 3-5 hours (using an att SIM)
cingular = 1 hour (using a cingular SIM)

i haven't figured out why, or if i'm doing anything to encourage or discourage these delay times. but hope this helps.